Sentence Correction

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.

were found to have increased difficulties

have been found to have increased difficulty

were found to have increasing difficulty

had been found to have increased difficulties

have been found to have increasing difficulties

pls explain yr pick...

C/E - increasing difficulty - wrong
D - had been - change in tense

A - were found - Past tense seems to mean that the pigeons now don't have any difficulty - wrong

Present perfect continuous is right as it started in the past and still continues.

IMO B

heymayank08 wrote: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.

were found to have increased difficulties

have been found to have increased difficulty

were found to have increasing difficulty

had been found to have increased difficulties

have been found to have increasing difficulties

pls explain yr pick...

Straight B.

[spoiler]OA : B[/spoiler]