it was only after he had spent several nights digging around the cross____he decided to write to jac

题目

it was only after he had spent several nights digging around the cross____he decided to write to jack williams to find out if he was wasting his time there.
A that B how C and which D what
the answer is A,tell mewhy and translate it ,thanks

答案

答案是A.
这是一个固定搭配,做强调使用.
固定词组：It was only after xxxx that
翻译为：只有当他花费了几个夜晚在十字路口徘徊后,他才决定写信给杰克 威廉姆斯,以知道他是否一直在浪费他的时间.