The reporter said that the UFO ________east to west when be saw it.
问题描述：
The reporter said that the UFO ________east to west when be saw it.
A．was travelling B．travelled
C．had been traveling D．was to travel.
为什么?
答
A when 引导时间状语 表当...时候,而那时候同时发生的事,则用进行时