Much should be use for uncountable and Many should be for Countable.
We say How many elephants do you have, not How much elephant.
So all option Which address number of elephant with "Much" is incorrect ?
So option B and C is wrong
Lets Do POE for rest,
A) covering as much as 90 percent of Thailand and accomodating as many as 300,000 elephants, a third of them
Covering and Accommodating - Modifier and hence we dont have verb in whole sentence.
B) covering as much as 90 percent of Thailand accomodated as much as 300,000 elephants, a third of them
Much is used to represent quantifiable noun Elephant
C) covered as much as 90 percent of Thailand and accomodated as much as 300,000 elephants, a third
Much is used to represent quantifiable noun Elephant
D) covered as much as 90 percent of Thailand and accomodated as many as 300,000 elephants, a third of them
Covered and accommodated - Verb for subject "forest" and both are in parellel
E) covered as much as 90 percent of Thailand and accomodating as many as 300,000 elephants, with a third of them
Accommodating - is modifier and does not have anything in parellel.
"With a third of them " - adverbial modifier phrase - Modifying verb "Covered and Accommodated (though we dont have accommodated verb it is wrongly mentioned as Accommodating ) Answer question related to verb such as How forest covered.
So it look like, How forest covered - it covered with a third of them ... truly illogical meaning