309. 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

Solution:

Tense*

A and D can be eliminated for the use of past tense as the use of “appears to” suggests that the research is ongoing. ‘Since’ is used as ‘because’ here and should not be considered to refer time.
‘Increasing’ suggests that the difficulty is continuing to increase which is obviously weird. Thus, C and E can be eliminated.
B is the best choice.

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