Unlike frogs that metamorphose from tadpoles into adults within a one-year period, it takes three to four years for the mountain yellow-legged frog of the Sierra Nevada to reach adulthood, and so they are restricted to deeper bodies of water that do not dry up in summer or freeze solid in winter.

(A) it takes three to four years for the mountain yellow-legged frog of the Sierra Nevada to reach adulthood, and so they are
(B) it takes the mountain yellow-legged frog of the Sierra Nevada three to four years until it reaches adulthood, and therefore it is
(C) in the Sierra Nevada, mountain yellow-legged tree frogs take three to four years to reach adulthood, thus being
(D) mountain yellow-legged frogs of the Sierra Nevada take three to four years until they reach adulthood, thus
(E) mountain yellow-legged frogs of the Sierra Nevada take three to four years to reach adulthood, and so they are

the OA is E
But aren't and and so both conj? I never saw people putting these 2 words together before.
and I think I've found the original source of this sentence in NEW York Time
http://www.nytimes.com/2000/11/28/scien ... wanted=all
"Also, unlike many other frogs that metamorphose from tadpoles to adults in one year, the high-elevation frogs take three to four years to reach adulthood, so they are restricted to deeper bodies of water that do not dry up in summer or freeze solid in winter. "

it doesn't have and before so in the original sentence.

Can anyone explain this to me?

Thanks a lot

this is where we step in with the following astonishingly simple, but 100% reliable, rule:

on official problems, CORRECT ANSWERS ARE CORRECT.

see here:
http://www.manhattangmat.com/blog/index ... -the-gmat/

the only way you can approach these things effectively is to say
"oh, ok, i didn't know you could do that"
and then add the example to your mental repository.

since the question is official, it's a complete waste of your time to continue doubting it after you've verified that it's the OA.

Hi
is d wrong because it is changing the meaning:
wording in d means that it takes 3-4 years to metamorphose until they reach adulthood, then they might take different time (differnent from 3 to 4 years) to metmorphose.

nah, not really. there are 2 things wrong with that choice, though.

* unidiomatic use of "until".
you can't say "you'll take X amount of time UNTIL..."
UNTIL is used after a description of an action: i will run until i become exhausted.
the correct idiomatic expression is "you'll take X amount of time to VERB," as used in the correct choice.

* the modifier doesn't make sense. since "(thus) restricted" functions as an adjective, this modifier (like all other adjectival modifiers) tags onto the preceding noun. therefore, this sentence is saying that adulthood is confined to deeper bodies of water, a nonsense statement.

Hi Ron -
In “E” the correct answer choice why “…adulthood, and” is correct? I have seen on the form in some other questions that if we don’t have a list of items we can’t use “ , and”. Can you please help me understand when this construction is acceptable?
I eliminated “E” right away because of this construction
Regards,

@Agha79,

And is a conjunction and is used to connect grammatically coordinate words, phrases, or clauses

e.g

He felt sick and decided to lie down for a while
He read for an hour and went to bed
They invited every Tom, Dick, and Harry to the party

List of items needs 'and' , as you said, because it includes grammatically coordinated words.

Caution --- > do not use 'and' with subordinate clauses.

Although, while etc....are subordinating conjunctions, and are used to connect subordinating clauses.

hi -

if you use "and" to connect two independent clauses (i.e., two constructions each of which is a complete sentence on its own), then it is normally preceded by a comma.

this is not a 100% rule; you'll occasionally see two independent clauses separated by just "and", without a comma. (usually, this only happens if the clauses are really short.) but it's the usual convention.