______is estimated that a round-trip to Mars would take more than a year.A,That
题型：不详难度：来源：
______is estimated that a round-trip to Mars would take more than a year.
A,That B,what C,There D,It |
答案
| D |
解析
试题分析：通过分析句子结构，可知句子的真正主语是that引导的主语从句，这里需要形式主语，故用it。
点评：动词不定式，动名词或主语从句作主语时，通常把它们放在谓语动词前，而用it作形式主语，放到句首。 |
举一反三
_____is today Britain used to be three different countries,and over many years the three countries became one.
A,It B,What C,Where D,As |
______the price of a shirt is low or not depends on the amount of material and labour involed in making it.
A,That B,What C,If D,whether |
It is obvious to the students______they should get well prepared for their future.
A,as b,which C,whether D,that |
_______was most important to her,she told me,was her family.
A,It B,This C,What D,As |
______is known to us all is that the 2008 olympic Games will take place in Beijing.
A,It B,What C,As D,Which |
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