what was it about snails that

It was about snails that made the writer collect them for his friend on that day in particular 意思是 作者在那天为他的朋友逮了许多的蜗牛 去掉it was about that,完整句子 所以是强调句 改成疑问句倒转前面你不能单独看about snails,要联系前面的it was用what是因为固定搭配,不用why这个句子是对snails提出质疑,为什么是蜗牛,而不是其他的动物的强调疑问句型。