Niagara Falls (is) not (only one) of (North America’s greatest) tourist attractions but (also source) of hydroelectricity.答案是D,为什么?我认为是A
11)Perhaps even more important than the accuracy and realibility of a m...cal instrument ___.
A.that positioning it is correct
B.is positioned correctly
C.that its correct position
D.is that it be positioned correctly
这个答案是什么呢?