The reporter said that the UFO _____ east to west when he saw it

The reporter said that the UFO _____ east to west when he saw it.
A、 traveled
B、 was traveling
C、 was to travel
D、 had been traveling
【正确答案】：B
【题目解析】：整句话的意思为：报道说，他看到UFO的时候，它正从东往西去。