大全309,主谓结构在哪里,牛牛帮帮忙

1.        For some birds the sense of smell appears to play a role in navigation, since pigeons with surgically removed olfactory nerves were found to have increased difficulties in homing.

(A) were found to have increased difficulties

(B) have been found to have increased difficulty

(C) were found to have increasing difficulty

(D) had been found to have increased difficulties

(E) have been found to have increasing difficulties

这道题目的判断的过程是怎么样的，特别是主谓结构是哪个。 各位牛牛们帮帮忙拉~！~！~！~！~！~

http://forum.chasedream.com/dispbbs.asp?BoardID=23&ID=57755

309, 补充-104

A) 时态错。appears一般时，不跟过去和过去完成。
B) best. have difficulty in固定表达; increased有表增加后结果的意味。
C) 时态错。
D) 时态错。
E) increasing有表增加正在进行的意味；difficulties错，应该是difficulty。

关键是最后条，顺便回答LZ问题，pigeons （with surgically removed olfactory nerves ）were found to

如果分析的不对，大家指点一二，谢谢