Kinds of sentences

Sentences fall into 4 groups:
declarative sentences that make a statement
My friend is a student.
interrogative sentences that ask a questions
Did you ask your teacher?
imperative sentences that give a command or make a request
Sound the alarm at once! (command)
Please read the information. (request)
exclamatory sentences that express strong feeling or sudden emotion
What a tragedy this is!

Another sentence pattern that we use frequently is the sentence that begins with the word there. When the word there is used to introduce the sentence, it is possible to place the subject after the verb.

A heavy frost was last night.
There was a heavy frost last night.

When the word there functions in this way, it is called an expletive.

It is important to transpose the sentence beginning with there in order to determinate the true subject of sentence.

There were 10 people in the room. (there - expletive)
There they are. (there - adverb of place)