Sentence is in present continuous tense.
Rule :
Subject + is/am/are + V-ing + other agents.
It’s not raining so we are not using an umbrella.

Sentence is in Future perfect tense.
Rule :
Subject + will/shall + have + V³ + other agents.
By the end of summer, you will have passed your higher secondary examination.

Sentence is in present continuous tense.
Rule :
Subject + is/am/are + V-ing + other agents.
Students are preparing for English Grammar as their exam is very near.

A baby was not eating sandwich at this time yesterday.

Sentence is in past continuous tense.
Rule :
Subject + was/were + V-ing + other agents.
He was too much busy as he was doing his home work.

When you are speaking of or for yourself, use "am." When you are talking about a person or a thing (in the singular), use "is." When you are talking to a person, and when you are talking about other people or things (in the plural), use "are." Here, it is plural as "books" is there in the sentence. Hence, are will be used.

I want to learn French language from the person who is experienced.

During --- throughout the course or duration of (a period of time).
My uncle died during the war.

Look, are these passengers waiting for a bus?

Sentence is in present continuous tense in passive voice.
Rule :
Subject + is/am/are + being + V³ + other agents.
Gifts are being distributed among the students now.

If you gulp down food or drink, you quickly eat or drink it all by swallowing large quantities of it at once.
The phrase ‘to gulp down' means to swallow eagerly.

Only the brave deserve the fair.

How nicely the vegetables were arranged in that shop!

How was your last question paper attempted?

Principle --- a fundamental truth or proposition that serves as the foundation for a system of belief or behaviour or for a chain of reasoning.
Do you know the principle of your religion?

With a positive sentence the interrogative part is always negative. Therefore, aren't they is the right option.

The person who talks too much is seldom respected.

If there is "when" then the sentence will start with "Hardly".
Hardly had it stopped raining when we started our journey.

She did not sing so well as her friend.

The driver could not control the bus, therefore the accident took place.

The higher we go, the thinner the air becomes.

Around --- located or situated on every side.
There is a fence around the pool.

"The" is a definite article which is used before a noun that is fixed, special or discussed earlier. "A/An" is used before an indefinite singular noun. "INS Vikramaditya" is a fixed noun. Hence "the" will be used.
The prime Minister dedicated the INS Vikramaditya to the nation.