You will want two trees about ten feet apart, from ________to suspend your tent.
A．there
B．then
C．which
D．where
正确答案：C
例题解析： 介词+关系代词+不定式作定语，只有which 是关系代词。

That was so serious a matter that I had no choice but ______the police.
A．called in
B．calling in
C．call in
D．to call in
正确答案：D
例题解析：Have no choice but 后要带接to 的不定式，意思是 只能……别无选择。

Americans eat ________as they actually need every day.
A．twice as much protein
B．protein twice as much
C．twice protein as much
D．protein as twice much
正确答案：A．
例题解析：译文：美洲人每天所食用的蛋白质是他们实际需要的两倍。倍数+as+形容词+as，表示倍数