Is this necessary to complete the design before the National Day?为什么是this而不是 it ,that,he?说出详细原因

问题描述:

Is this necessary to complete the design before the National Day?为什么是this
而不是 it ,that,he?说出详细原因

it this that可以互换,看哪个更符合语境或语感。

错了吧,it is +adj to do sth是固定用法,it作形式主语