关于主语从句It is...that...
有个句子：
It is the season ____ the place is full of flowers.
A.where B.when C.wherever D.that
我觉得应该选 D.that
可是参考答案是 B.when
有没有人帮我解答一下到底选哪个正确呀,理由详细点最好.