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...
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...
