they tried to find out_________the new train had gone.

问题描述:

they tried to find out_________the new train had gone.
A how long
B how far
选哪个为什么
另外一个why 不选

选B,因为A虽然也是说 距离长短 的短句,但是它主要 adj 的是一个固定物体的长短
而B选项是形容通过距离的长短,符合句意