use will word (by
answer depends on context
The answer depends on context .If i say i came in a car.Then i am correct.It also depend on the dimension of the Noun.
Pretty much everything but on is correct.
I will always go for "by" because of its flexibility, on a bus it correct but u cant use "on a" or "on" for 2buses, finally "on the" can only be correct only if you are referring to a particulay bus.