For some birds the sense of smell appears to paly 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
答案是B,我选的A。不明白为什么要用现在完成时,而且感觉困难应该是复数。麻烦老师讲解。
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【请May老师回答】这题鸡精提供的答案是D 可是我觉得第二个条件不能得出呢 假设n三次方是x平方 除以n平方 是可以得到x/ n 平方 但是x/n 不一定是整数呀?