Option A:
Two new studies (Subject of the Main Clause) indicate (Main Clause Verb)
that ( starting of Dependent Clause)
Many people ( Subject of DC)
{ become ( Verb of DC) Obese }: Verb Phrase
more ( Comparison structure: more -than) :
1) due to ( prepositional phrase) the fact that [their bodies burn calories too slowly ( too slowly is the adverb for burn)]: DC
than ( Comparison Structure: more - than)
overeating ( Gerund Noun )
Errors:
Meaning issue:
The meaning of the sentence is Two studies have indicated that people become obese more because they are losing less weight than because they are eating/gaining more.
However, option A's comparison structure cannot convey that meaning.
Grammatical issue:
The "more - than" parallel is wrong here.
Many people become obese
: more due to the fact...........
: than overeating: Makes no sense ( Many people become obese overeating)
Option B:
Due to their burning calories too slowly: Wrong.
1) It seems like due to "their bodies", everything is happening.
Also the parallel :
than
" to eating too much " is wrong ( Many people become obese to eating too much : Wrong)
Option C :
Structure-wise issue: Wrong parallel again ( same as options A and B)
Also
meaning wise parallelism is slightly missing.
Their bodies burn calories too slowly.
They are overeaters ( Could have been better, Had this been " they eat too much" )
Option D: Corrected all the errors mentioned above.
Option E:
GMATNinja explained already.