What can we do to keep the air clean?

A cart driven by oxen or bulls is known as :

How many wheels does a train have ?

Which among these is a land transport ?

Which invention changed the way of travel?

Trains arrive at and leaves from:

People sits on carts drawn by bulls, horses or camels in:

We could go to some countries by:

Which is the most commonly used means of  air transport?

Helicopters and aeroplanes are called :