When and where this took place ____ still unknown.

题目

When and where this took place ____ still unknown.
A：has B：is C：were D：are

答案

B:is
解释： when and where this took place
是个整体,句子的意思是：（这个事情什么时候在哪发生 ）仍然不被人知,括号内这个整体不被人知道,所以必然是用is , 时态有后边的still unknown可知用一般现在时