83. 

The number of plant and animal species that humans are known to have forced to extinction in the last half millennium is over 800.

(A) humans are known to have forced to extinction

(B) humans are known as having forced to become extinct

(C) humans are known for forcing to become extinct

(D) are known that humans forced to become extinct

(E) are known as having been forced to extinction by humans

答案是A， 但是结构不是很明白

请大家指点一下这个句子的结构，that同位语从句中 are known to（世人皆知？） 是个什么结构？不是很明白

OG 10th SC49:

49. The cameras of the Voyager II spacecraft detected six small, previously unseen moons circling Uranus, which doubles to twelve the number of satellites now known as orbiting the distant planet

(A)  which doubles to twelve the number of satellites now known as orbiting

(B)   doubling to twelve the number of satellites now known to orbit

(C)  which doubles to twelve the number of satellites now known in orbit around

(D)  doubling to twelve the number of satellites now known as orbiting

(E)   which doubles to twelve the number of satellites now known that orbit

In A, C, and E, which seems to refer to a vague concept invol­ving the detection of moons, but there is no specific noun, such as detection, to which it can refer.

Also in E, the use of the phrasing the number... now known that orbit is ungrammatical and unclear.

B and D use the correct participial form, doubling, to modify the preceding clause, 现在分词表示伴随的结果

but D, like A, uses known as orbiting rather than known to orbit, a phrase that is more idiomatic in context. B, therefore, is the best answer.

1。首先是词组的用法

quoted from Longman:
be known to do something
- Smoking is known to increase a person's risk of developing lung cancer.

2。句子结构

这个句子that引导的从句中，that是做have forced的宾语，而从句不是主语。还原之后为：

people are known to have forced plant and animal species (that指代) to extinction....

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