Which of the following sentences is imperative ?
A) He took less than ten minutes to finish this test.
B) Is this an interrogative sentence ?
C) Mark the sentence below as imperative.
D) The students should respect their teachers.

Dear Student,

The sentence which is used to convey a command, a request, or a forbiddance is called an imperative sentence. Here, C) Mark the sentence below as imperative is an imperative sentence as it commands the reader.
Explanation: A) He took less than ten minutes to finish this test. is a declamatory sentence
B) Is this an interrogative sentence ?  is an interrogative sentence. 
D) The students should respect their teachers. may also seem like a command but it still gives the students a choice due to the use of the word 'should'. Therefore, it is not considered as an imperative sentence. 


Regards