求助GWD-17-32

32. GWD17-Q32:

Navigators have known for thousands of years that the ocean has variable currents, but it is only in the last half century that a reasonably clear picture has emerged of the patterns and causes of ocean currents.

1. a reasonably clear picture has emerged of the patterns and causes of ocean currents

2. a reasonably clear picture of the patterns of ocean currents and their causes have emerged

3. a reasonably clear picture emerged of ocean currents, their patterns and the causes of them

4. there have emerged a reasonably clear picture of the patterns of ocean currents and what caused them

5. there had emerged a reasonably clear picture of the patterns of ocean currents and their causesi

答案是A。

一直想不通在这里‘has emerged' 是否可以和'inthe last half century' 一起用?明明是过去,为何用现在完成时? 难道'in the last century' 表示的是大段时间,而不是一个时间点?

LZ说得很对。

with in the past/last/recent  N years        (N代表一个数或一段时间)

in the past/last/recent  N years       

都是用现在完成时

谢谢指点

这题我不是很明白，这里的A感觉不对，a reasonably clear picture has emerged of the patterns and causes of ocean currents感觉不符合语法规则啊。 emerge是不vi，都是sth emerge；cause是vt，都是加直接宾语的，那这些是怎么回事啊？

B感觉就很舒服，a reasonably clear picture of the patterns of ocean currents and their causes have emerged，就完全没有A的问题，那么A为什么是对的，B为什么不对哪？是不是因为their 没有指带？

B选项犯了Agreement的错误啊

主语是a reasonably clear picture，（虽然of了一堆），结果后面用了have……

可否认为是 a picture and their causes 作复合主语？

关于B: a reasonably clear picture of （the patterns of ocean currents and their causes ）

a picture of 后面貌似应该包含两块内容：1是the patterns of ocean currents , 2是their causes ；它们统统在picture下面，是picture的从属成分，

如果是a picture and their causes 作复合主语，their就显得不太合理了，我觉得之所以用their（指代patterns) ，是因为它修饰的成分和the patterns of ocean currents 并列...

这是我的理解，不只对否~