<ol>
<li>Twice as many bird species inhabit Ecuador (as in) North America.</li>
</ol>
<p>A) as in
B) as inhabit
C) instead of in
D) when compared to
E) than</p>
<p>I know that the last three are not right, but I can't decide whether it is A or B.</p>
<ol>
<li>(Although) familiar to us (from representations) in ancient art, war chariots are rare museum artifacts (because by) the sixth century B.C. they were (no longer) used in battle. No error (E)</li>
</ol>
<p>I thought it was A because the ideas were not opposing. Turns out it is E. Can anyone explain please?</p>
<p>1.
You can tell A is wrong because the structure would not be parallel. If an “in” introduces the second country, an “in” would have to introduce the first. Since it doesn’t, A is wrong.</p>
<p>Since parallelism here requires an ‘as,’ which you’ve noted, B must therefore be correct. B is primarily correct because the “as many” phrase describes birds, not what the birds are doing. If the second part is going to omit the subject “birds,” then it must explicitly repeat the verb “inhabit.”</p>
<p>2.
The ideas ARE opposed: familiar in art, rare in museums. This is a case where the sentence does not try to be parallel, and there is no reason why it should be parallel. I say that because I’m guessing that’s why you did not recognize the familiar-rare contrast.</p>