Question

Fill in the blank with the most appropriate word.
A thermostat is something ________ controls temperatures.

• A. who
• B. where
• C. when
• D. which

Answer 1

The correct option is D which

Relative pronouns have two functions- Like other pronouns they stand for a noun or pronoun placed before them and like conjunctions they join subclauses with main clause and start the adjective clause.

In the given sentence the subject is a thermostat.

'Which' is used for things and animals.

'Who' is used for people.

'When' is used to indicate time.

'Where' is used in case of places.

Since the given sentence describes a thing, 'which' must be used.

Thus option D is the correct answer.

Options A,B,C are incorrect.