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标题: 关于时态的问题，GWD17-Q32 [打印本页]

作者: soojin3215 时间: 2011-3-2 20:06 标题: 关于时态的问题，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.

A) a reasonably clear picture has emerged of the patterns and causes of ocean currents
B) a reasonably clear picture of the patterns of ocean currents and their causes have emerged
C) a reasonably clear picture emerged of ocean currents, their patterns and the causes of them
D) there have emerged a reasonably clear picture of the patterns of ocean currents and what caused them
E) there had emerged a reasonably clear picture of the patterns of ocean currents and their causes

答案是A，我的疑问是既然发生在“ in the last half century”，为什么要用完成时，不用过去时？

作者: swlfxer 时间: 2011-3-3 06:48

in the last century, lz要记住哦，是大段时间，要用现在完成时
用现在完成时的标志：
1. since
2. 大段时间如in the pat several years, in the last century, in a period of time
3. 出现has ever seen或者than ever before possible等字眼

作者: soojin3215 时间: 2011-3-3 20:05

啊，终于明白了，谢谢，所以下面这句也是这个原因才用完成时的吗？

All Y chromosomes in existence today are descended from a single ancestor’s who is thought to have lived about 140,000 years ago.
A) a single ancestor’s who is thought to have lived
B) a single ancestor’s who was thought to live
C) a single ancestor whom it is thought had lived
D) the Y chromosome of a single ancestor who is thought to have lived
E) the Y chromosome of a single ancestor whom it was thought had lived

作者: ozymendias 时间: 2011-3-4 21:41

但是不懂的是 but it is only last half century 里面为什么用IS而不用WAS呢？

作者: soojin3215 时间: 2011-3-5 08:52

这个我知道，因为是强调句 it is ... that... 还原就是
in the last half century，a reasonably clear picture has emerged of the patterns and causes of ocean current

作者: angelsgx 时间: 2011-3-6 14:23

in last century和in the last century有区别。
in the last century是指到这一瞬间截止，往前倒数的一个世纪，即1911年1月27到2011年1月27.（当然对于大范围时间不必如此精确）
而就我们这个时间2011年1月27号来言，in last century就是指20世纪了.

作者: angelsgx 时间: 2011-3-6 14:26

啊，终于明白了，谢谢，所以下面这句也是这个原因才用完成时的吗？

All Y chromosomes in existence t ...
soojin3215 发表于 2011-3-3 20:05

is thought to have done中have done其实是表示往前推一个时态，来区分is thought to do，因为to后面一定要跟动词原型，所以要做如此区分，所以，have done并不是表示完成时。

作者: soojin3215 时间: 2011-3-7 06:47

可不可以理解为in last century 用过去时in the last century用完成时？

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