When you called me this morning ,I happened -------a meeting Ato be having B.to have

When you called me this morning ,I happened -------a meeting Ato be having B.to have
When you called me this morning ,I happened -------a meeting Ato be having B.to have

When you called me this morning ,I happened -------a meeting Ato be having B.to have
When you called me this morning ,I happened to be having a meeting
Ato be having B.to have
我是英语教师,不明的可再问.

to be having

A to be having