RiyaR wrote:36. 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

The answer in this case is D-which I did not get how. Isnt the beginning og the phrase "to produce" incorrect?

(a)/(b)- use of "and" is incorrect --mining heat and electricity generation are not 2 independent concepts in which the scientists have succeeded for the first time instead one leads to another.
(c)/(e)- there's parallelism at the end of underline part and these options fail there
(e)- placement of "enough" is awkward comparative to (c)&(d)

also use of "for" in (c) sort of implies reason why scientists succeeded.

use of "to produce" is the best here.

This is a classic parallelism problem, touching upon simple vs complex gerunds. Simple gerunds such as "verb-ing" should never be parallel to complex gerunds such as "the/a/an+ verb-ing + of the..". Once you know this, B starts to look awkward and unparallel.

Mining heat from X to produce Y

"and" --> incorrect here.
See why "and" is inappropriate here
have succeeded for the first time in mining heat from the Earth's interior and producing energy on a commercial scale
=
succeeded for first time in doing X and doing Y.

above sentence is grammatically correct.. but logically doesn't make sense.

it means first time producing energy on commercial scale but that's not intention of author.
..[ energy might be produced on commercial scale by other methods ...]
first time in doing X from Z to product Y.
Between D and E.
D looks better.

A. and producing energy on a commercial scale, enough for efficient generation of electricity and heating --> Misplaced modifier. The modifier is modifying "commercial scale" where it should be placed near "energy". Also, "for efficient generation of electricity" and "heating" are not parallel. It should have been "for generating electricity and heating ". This sentence also perverts the intended meaning. The sentence should have been "Scientists at the Los Alamos National Laboratory have succeeded for the first time in mining heat from the Earth's interior to produce energy on a commercial scale,"

B. and producing enough energy on a commercial scale for electricity to be generated efficiently and to heat--> again it should be "to produce" and the underlined parts are not parallel.

C. for energy production on a commercial scale, enough for generating electricity efficiently and to heat--> underlined parts are not parallel.
D. to produce energy on a commercial scale, enough for generating electricity efficiently and for heating--> looks good. Underlined parts are parallel and "and" replaced by "to".

E. to produce enough energy on a commercial scale for efficient generation of electricity and heat --> underlined portion is wrong. It should be a noun / noun form (gerund) - "heating". Option E also changes the intended meaning of the sentence. Placement of enough is awkward here.
It should be D.