We just ______ to catch the bus 是填in time还是on time

We're just （in time） to catch the bus.句意：我们及时赶上了公共汽车.
in time有"及时;迟早"的意思,意指正赶上时候或恰在需要的时候,或解释为"终有一天;最后";
on time是"准时;按时"之意.如:
We were just in time for(或to catch) the bus.(我们及时赶上了公共汽车)
The train pulled in on time.(火车准时到站了)

on time.不要问我为什么。