一道英语选择题(要说明理由)!When you called on me ,I was __ a visit to Mr.SmithA.on B.at C.in D.to

一道英语选择题(要说明理由)!When you called on me ,I was __ a visit to Mr.SmithA.on B.at C.in D.to
一道英语选择题(要说明理由)!
When you called on me ,I was __ a visit to Mr.Smith
A.on B.at C.in D.to

一道英语选择题(要说明理由)!When you called on me ,I was __ a visit to Mr.SmithA.on B.at C.in D.to
be on a visit to =visit
参观

A
固定搭配！on a visit~

恩我都是选A的

a 表示处于某种状态中,而且这是固定搭配on a visit.