either a noun or a verb
The preposition is through.The noun 'tunnel' is the object of the preposition.Through
"By" can be an adverb, as in "We watched the train go by." "By" can also be a preposition, as in "We stayed in a cottage by the sea."
Yes, it can be. But it can also be an adverb ("Come aboard"). It refers to riding in or on a vehicle, such as a ship, plane, train, or bus.
If you mean 'What preposition would you use to describe train travel?' the answer is 'by': 'I will go by train when I visit my aunt in Edinburgh.' However, 'train' has other meanings, for example, to prepare for something. In that case it is a verb, not a noun. So you would say 'The athlete will train for the Olympics.' You will get a much better answer if you express your question as a complete sentence. It is also more considerate towards the people who you hope will help you. I have made two guesses at what you might mean, but both of them may be wrong. I should not really have to spend time guessing what you mean.
Yes, it is one word "aboard" -- as an adverb or preposition, it means "on board" a vehicle such as a bus, train, plane, or ship.
We use "in" for a smaller, enclosed space like a car, but "on" for a larger, open transportation mode like a train or plane. The choice of preposition reflects the size and openness of the vehicle.
No, then is not a preposition. It is a conjuction.Than is a preposition.
flew is not a preposition. sorry but through is a preposition
No, then is not a preposition. It is a conjuction.Than is a preposition.
its a preposition
At is a preposition. Anything that can be ___ the box is a preposition. For Example: At the box.
If is not a preposition. It is a conjunction.