请问专家:bus plane train ship boat car taxi前用in 还是on?谢谢帮忙!

一般用by,也可以换成介词，用on还是in，请看下面的具体搭配：
by car=in a car（或in the car,in sb's car,其它词类似）
by taxi=in a taxi
by train=in a train
by ship=on a ship
by boat=in a boat
by bus=on a bus
by plane=on a plane

另请你顺便注意你没有问到的词：
on foot
by bicycle=on a bicycle
by air 空运
by land 陆运
by sea 海运
on horseback
by phone
by letter
by radio
by air mail
by hand