First, see the non-underline part: "...than
itscousin..." ==> The subject MUST be singular ==> C, D are out immediately.
Equally at ease scrambling up the craggiest and treacherous mountain landscapes as perching on a ready-made barnyard knoll; the goat is considerably more adaptable than its cousin, the sheep.
A -
Equally at ease scrambling up the craggiest and treacherous mountain landscapes as perching on ready-made barnyard knolls; the goat is
Wrong. The part before the semi colon MUST be a complete sentence. In addition, it MUST be a main sentence, the sentence before the semicolon is dependent sentence.
B - The goat, as comfortable scrambling up the craggiest, most treacherous mountain landscapes as to perch on ready-made barnyard knolls,
it is
Wrong. The phrase "as comfortable....knolls" is modifier. If you remove it, the sentence still makes sense. Let remove the modifier and see: The goat,
modifier, it is.... ==> "it" is placed wrongly.
C - As comfortable when scrambling up the craggiest, treacherous mountain landscapes as when perching on ready-made barnyard knolls, goats
areWrong. "are" is wrong.
D - Equally at ease scrambling up the craggiest and most treacherous mountain landscapes as they are perching on ready-made barnyard knolls, goats
areWrong. "are" is wrong.
E -
As comfortable scrambling up the craggiest, most treacherous mountain landscapes
as perching on ready-made barnyard knolls, the goat
isCorrect. - Good comparison:
as scrambling......
as perching.......
- Good S-V agreement: The beginning part is modifier. The goat
is singular --> correct.
Hope it helps.