some birds the sense of smell appears

[nick_zen]

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

please let me know line of reasoning and answer

[defylogic]

My choice, B.
First part uses simple present, use of simple past and past perfect in the following part is illogical. This leaves us with options B and E. Though both increased and increasing are adjectives, E makes less sense as it suggests that the difficulties are increasing.

[mannu08]

IMO answer is B.

@nick: OA please.

[nick_zen]

OA is B.

thanks