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 (E) have been found to have increasing difficulties
这题答案给B，我觉得这里have been 完成时没有必要。用过去时好，表达在过去发生，我选A 请指点
1,there is only one difficulty----homing,so difficulties are wrong. 2,form context, the main clause is just a conclusion of the (since pigeons with surgically removed olfactory nerves were found to have increased difficulties in homing.) namely,it is the sub-clause influence the main clause,the usage of 完成式 is perfect!
以下是引用nina23在2003-11-5 22:01:00的发言： 1,there is only one difficulty----homing,so difficulties are wrong. 2,form context, the main clause is just a conclusion of the (since pigeons with surgically removed olfactory nerves were found to have increased difficulties in homing.) namely,it is the sub-clause influence the main clause,the usage of 完成式 is perfect!
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发表于 2003-10-27 15:37:00
