to be - function in the sentence

Identify the function of the verb “to be” in the sentence:

She is happy.

Identify the function of the verb “to be” in the sentence:

 We are studying now.

Identify the function of the verb “to be” in the sentence:

These letters are written every day.

Identify the function of the verb “to be” in the sentence:

He is to come tomorrow.

Identify the function of the verb “to be” in the sentence:

 I was in the park.

Identify the function of the verb “to be” in the sentence:

They are playing the guitar.

Identify the function of the verb “to be” in the sentence:

The room is cleaned every morning.

Identify the function of the verb “to be” in the sentence:

You are to help him.

Identify the function of the verb “to be” in the sentence:

She was my friend.

Identify the function of the verb “to be” in the sentence:

 The children are sleeping in their beds.