Which of the sentences below are correct?
This’s my best friend, William.
Those’re my classmates, James and Harry.
That’s my teacher, Mrs Wilson.
UPDATE: I just took an exam. The correct sentence is the last one, but I don't understand why.
Which of the sentences below are correct?
This’s my best friend, William.
Those’re my classmates, James and Harry.
That’s my teacher, Mrs Wilson.
UPDATE: I just took an exam. The correct sentence is the last one, but I don't understand why.
All three are grammatically correct and can be used to introduce persons, but only That’s my teacher, Mrs. Wilson. is normally written. The first two are uncommon contractions in those sentences.
Which demonstrative pronoun you use is a matter of context.
This implies that you're standing or sitting close to your best friend, or else pointing to a picture of him.
Those implies that your classmates are farther away from you than your best friend is, or in a different part of the picture. Some native speakers might use these and others might use they. That also suggests that your teacher is more distant from you than your best friend is.
You might also being using different pronouns because you like variety and don't want to say this every time.
I see nothing wrong with using this for a person. Basically, this can be used to point out anything nearby. If a person is near you, you can introduce him by pointing with this.