-where is my pen.It's not ___I have left it.

问题描述:

-where is my pen.It's not ___I have left it.
-Maybe someone has mistaken it.
A.there B.where C.here D.place where
选哪个?要详解.

肯定是B.
is 是be动词,后面接表语从句.能引导表语从句只有里面的B.
而且这里 where = the place where.D缺少了the