The Chicago and Calumet Rivers originally flowed into the St. Lawrence by way of Lake Michigan, but having been redirected by constructing canals so that the water now empties into the Mississippi by way of the Illinois River.
A. Rivers originally flowed into the St. Lawrence by way of Lake Michigan, but having been redirected by constructing
B. Rivers had originally flowed into the St. Lawrence by way of Lake Michigan, but they have been redirected by constructing
C. Rivers, which originally flowed into the St. Lawrence by way of Lake Michigan but have been redirected by the construction of
D. Rivers, originally flowing into the St. Lawrence by way of Lake Michigan, but having been redirected by the construction of
E. Rivers, originally flowing into the St. Lawrence by way of Lake Michigan, have been redirected through the construction of


whats wrong with B..

have been redirected through the construction ??

Is it possible to use

HAD and HAVE in the same sentence.... as is done in B... or should we use past tense and present perfect for such situations.

or is there a definite rule -- that have and had can not be in the same sentence... only had and did are allowed ???




apart from the "to have" construction

IS OA:E???

there are two things wrong with (b).

one:
the use of the past perfect (had flowed) is inappropriate, because there is no second past-time marker or event to which this first event is relevant.
compare: the rivers had originally flowed into the st. lawrence, but then their course was diverted by...
the correct tense to use here would be the simple past, because this is the only past time frame referenced in the whole sentence.

two:
'by constructing' seems to refer back to the rivers as its ostensible subject, implying (absurdly) that the rivers themselves constructed the canals.

What is the right answer ?

IS the right answer : E

Yes

can somebody explain what's wrong with C

(c) isn't even a sentence. it's a really, really, really long sentence fragment.

the part in, and following, "which" is all one huge modifier:
which originally flowed ... but have been redirected...

there's no main verb.

if you don't see what i'm talking about, email back and i'll explain in further detail.

_________________
Being well-dressed gives a feeling of inward tranquillity [that] religion is powerless to bestow.
C.F. Forbes

D. Rivers, originally flowing into the St. Lawrence by way of Lake Michigan, but having been redirected by the construction of

What is wrong w/ D? How do I interpret the 'having been' construction?

Option D is again long sentence fragment.
Rivers, modifier, but modifier...

Ron,
I just wanted a clarification regarding your explanation for option b.
<two:
'by constructing' seems to refer back to the rivers as its ostensible subject, implying (absurdly) that the rivers themselves constructed the canals.>

the construction "they have been redirected by constructing ..". This is passive voice construction, so how could 'by constructing" refer back to rivers. I mean that rivers may be redirected by doing something, so how rivers can redirect themselves with this sentence construction..??

idiomatically, "BY ___ING" retains the subject of the preceding clause. this is something you just have to know.
it is also something of which most native speakers are aware, even though they can't actually articulate it. (this is the case for a great many, if not most, usage and idiom rules, actually.)
examples:
i am bored by performing jazz --> this means i get bored when i PLAY the music MYSELF.
i am bored by the performance of jazz --> i don't like to sit and listen to someone else play jazz.

same deal here.

_________________
Being well-dressed gives a feeling of inward tranquillity [that] religion is powerless to bestow.
C.F. Forbes

there are two things wrong with (b).

one:
the use of the past perfect (had flowed) is inappropriate, because there is no second past-time marker or event to which this first event is relevant.
compare: the rivers had originally flowed into the st. lawrence, but then their course was diverted by...
the correct tense to use here would be the simple past, because this is the only past time frame referenced in the whole sentence.

but you see this question and pay attention to the tense

Ozone, a special form of oxygen that screens out harmful ultraviolet rays, reaches high concentrations twelve miles above Earth, where it has long appeared that it was immune from human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer.
(A) has long appeared that it was immune from
(B) has long appeared to have been immune from
(C) has long appeared as being immune to
D) had long appeared immune to
(E) had long appeared that it was immune to


ans:D

why use "had appeared " here??

The success of the program to eradicate smallpox has stimulated experts to pursue something they had not previously considered possible-better control, if not eradication, of such infections as measles and yaws.(Source: GMATPrep)

Ron, you see, past perfect is just there without simple past. could you explain in advance.

_________________
stephen

see here:
post35940.html#p35940

once you've looked at that:
stimulation is a point event. for the same reasons mentioned in that post, "has stimulated" actually signifies a past event (perhaps from the very recent past, but from the past nonetheless).

_________________
Being well-dressed gives a feeling of inward tranquillity [that] religion is powerless to bestow.
C.F. Forbes

Ron, to your point, HAVE BEEN REDIRECTED is not a single point event because 'BEEN' signifies progress, right? Could you please confirm my reasoning?