'They' is a third-person plural pronoun
Answer: A
Explanation.
In English language, The first person is referred to as the person who starts the conversation to the other.
The second person is the one to which the first person speaks.
The third person is the one who grasps the conversation from the other two and states without quoting the first person.
Here - a. 'They' is used to describe more than one person, so it is plural. 'They' is not used by first or second person, instead the third person uses it in his language. So it is third-person plural
b. 'we' is plural. 'We' is used by first-person and is a plural term- so it is a first-person plural
c. 'he' is singular stating a single person and it is used by a third person- so it is 3rd person singular
d. 'I' is singular and used by first person- so it is first-person singular.