Select the most appropriate option to fill in the blank.

We are planning to go to Delhi ______ train.

by

The most appropriate option to fill in the blank is by.

The word "by" means to travel or be conveyed in a particular means of transportation. This is the most appropriate word because it accurately describes how we are planning to go to Delhi. We are planning to travel to Delhi by train.

The other options are not as appropriate.

• On means in or onto the surface of something. It does not make sense in the context of the sentence, because we are not planning to travel to Delhi on the train.
• Of means belonging to or connected with someone or something. It does not make sense in the context of the sentence, because we are not planning to travel to Delhi of the train.
• At means in a particular place or position. It does not make sense in the context of the sentence, because we are not planning to travel to Delhi at the train.