104. 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

正确为B。 但是B用的是现在完成式，好像A中用的过去式不是更好嘛？"increased difficulity in" 与 "increased difficulities in"有什么不同嘛？ 谢谢

Since in the tense of the main sentense is present simple, it's more appropriate to use the present perfect in the dependant clause than to use past simple. difficulties is the plural form of difficulty.

1，注意前后时态的照应。

2， 用复数的困难没有必要。