Question

Few words which are used in both singular and plural but form cant change

Answer 1

Accommodation
Advice
Alms
Aircraft
Aluminum
Barracks
Bison

Answer 2

Perception verbs are certain words in a language that are used to indicate actions involving the senses or the ability to perceive the surrounding world.

Hear, see, watch, notice and similar verbs of perception can be followed by object + infinitive without to or object + -ing form.

There is usually a difference of meaning between the two structures.

The infinitive is used after these verbs when we want to say that we hear or see the whole of an action or event. The –ing form is used to suggest that we hear an action or event in progress.