Was it last Friday ________ you met him A.that B.on

Was it last Friday ________ you met him A.that B.on which C.which D.when
Was it last Friday ________ you met him A.that B.on which C.which D.when
that
想知道为什么不能是 when 不能看做是定语从句吗 It was last Friday when you met him.这个句子貌似也没错吧 last friday 做了先行词when引导的时间定语从句修饰last friday.
我知道这是个强调句型,应该选A,但是我想知道这个题为什么不能从时间定语从句的角度解答.