We regard ____to learn English grammer.A.it necessary B.it as necessary为什么答案选B?

是一种习惯用法吧.例如：
Do you regard it as necessary that we should come too? 你认为我们也有必要去吗?
Do you regard it as necessary I should come? 你认为我有必要来吗?
They regard the problem as not worthy of serious consideration. 对这一问题他们都认为不屑一顾.
比较一下：
I regard creativity both as a gift and as a skill. 我认为创造力既是一种天赋也是一种技巧.
Farmers regard foxes as vermin. 农夫把狐狸看成是*.
You shouldn't regard such important work as a trifling matter. 你可不能把这样重要的工作当儿戏.
Defenders of the death penalty clearly regard it as the ultimate deterrent. 支持死刑的人显然认为死刑是最具威慑力的刑罚.
如果能帮到你就请采纳.不可以把it理解为宾语，necessary理解为宾语补足语吗看来是不可以。英语句子就是那么用的，所以还是最好从英语吧。用“金山词霸”查了一下regard it necessary，也没有这样的例句。