Scientists at the Los Alamos National Laboratory have succeeded for the first time in mining heat from the Earth’s interior and producing energy on a commercial scale, enough for efficient generation of electricity and heating factories and homes.
A. and producing energy on a commercial scale, enough for efficient generation of electricity and heating
B. and producing enough energy on a commercial scale for electricity to be generated efficiently and to heat
C. for energy production on a commercial scale, enough for generating electricity efficiently and to heat
D. to produce energy on a commercial scale, enough for generating electricity efficiently and for heating
E. to produce enough energy on a commercial scale for efficient generation of electricity and heat

Why is A wrong ...
I thought mining is || to producing

Also--
enough for efficient generation of electricity and (for) heating ... can we say the second for is implied in A???

I think meaning-wise, "mining...to produce..." is better than the parallel structure "mining...and producing..." because "mining...to produce..." shows the purpose of "mining...".

If you try to make the sentence parallel, then you can read the sentence as
Scientists at the Los Alamos National Laboratory have succeeded for the first time in producing energy on a commercial scale.

Then, it seems that "producing energy on a commercial scale" has no relationship with "mining..."

Just my 2 cents.

I have always found that it is important to understand the complete meaning of a sentence like this to figure out as to where the parallelism lies.

In this sentence the scientists have succeeded in mining heat * to produce energy
It is important to understand that it is heat that is mined helps to produce energy.

Moreover Mining heat on a large scale maybe something innovative
But we do know that producing energy on large scale is not innovative ...

So A B and C are out

Between D and E

I'd vote for D b/c of parallelism between for X and for Y

Also in E enough energy on a commercial scale for x and y is awkward

My 2c

I am a bit confused.
What is the sentence trying to say?
Is it that scientists succeeded in mining for the first time or mining to produce commercial energy for the first time(means they had mined before)
I think whether we choose to use "and" or "to" depends on that.
Expert help needed please:)

that's a clarity issue; the fact of the matter is that both interpretations make sense.

but here's the zinger:
CORRECTNESS COMES BEFORE CLARITY.
if you can resolve the ambiguity simply by eliminating grammatically incorrect answer choices, you won't have to worry about deciding between the two meanings.
this is what happens here: both sentences having the first meaning (mining ... AND producing), while that meaning makes sense, are incorrect because of faulty parallelism. choice (a) puts for efficient generation in parallel with heating, and choice (b) puts for electricity to be generated in parallel with to heat.

in fact, based on grammatical parallelism alone, choice (d) is the winner; all the other choices exhibit blatant nonparallelism.
in cases like this, it's a waste of time even to consider subtleties of meaning; there's no point in agonizing over the meaning of a sentence with bad grammar.

Why is e wrong? Could "to produce" be parallel to "heat" (the to is implied)? Is the problem w/ "e" a change in meaning? Thanks

yes.

two ways you could look at it, both of which reach the same conclusion anyway:
(a) the logical parallelism is between generating electricity and heating homes/factories. therefore, any construction that creates parallelism between elements other than these is incorrect.
or
(b) the parallelism in the original choice, which makes sense and therefore must be followed, is between those two things. therefore, any answer choice putting other elements in parallel constitutes an unacceptable change in meaning.

either way you will conclude that (e) is incorrect.