．The reporter said that the UFO ________east to west when be saw it.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.a or dand why a or c

I Wonder whether there is a mistake in this sentence.I can't understand what's the meaning of "when be saw it". Or it may be written uncorrectly. I think C is the best answer.
The direct speech is "The UFO was travelling east to west when he saw it.'When it is put into the clause "the reporter said",the verb should be changed into "had been travelling".

C

A.
过去进行时.
当他看到的飞碟的时候,飞碟正从东向西飞行.
d 的话,语法都不对.如果改成 was going to 是说它正要从东向西飞行,也就是说它还没有开始飞.
但看上下文,一定是说飞碟正在移动,所以说.它正在从东往西飞.

A， 就是说他当时看见UFO时，这显然是过去， 就在过去的某一时刻， 另一个动作当时正在进行（UFO正从东向西飞行）， 所以要用过去进行时