两道SC问题

redli

1）repelled by bodily punishments such as maiming and branding, (the idea of penitentaiaries were reforms of the penal system by Quakers.)
c)Quakers suggested the penitentiary as a reform of the penal system.
d)Quakers suggested that the penal system be reformed as penitentiaries .
问题：选C，为什么D不可以，错在哪里？

2)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.
B)have been found to have increased difficulty.
问题：选B，原句错在哪里？为什么一定用过去完成时，DIFFICULTY一定要用单数。

猫猫头

1、抽象名词优于从句
2、前面是现在时呀，而且句子中并没有明确的点提示你这是发生在过去

redli

第二题，
1）觉得过去时也没什么错，即“已经被发现”，因其前面跟了个结论“For some birds the sense of smell appears to play a role in navigation”
2）除了时态，difficulty在单复数上有什么区别？

开若兰

QUOTE:

以下是引用redli在2002-11-16 16:16:00的发言：
2) 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.

QUOTE:

(B) have been found to have increased difficulty.

(E) have been found to have increasing difficulties

请教：为什么(E)选项错误？