Answer: c. force to suffer through
Explanation:
In the sentence, the definition that fits subject as it is used in the sentence above is to force through something.
In the sentence, subject is used as a verb and it simply means to force someone to undergo an unpleasant experience or an unpleasant treatment.
The sentence simply means that the teacher gives them difficult assignments which the students find tough and challenging.
Therefore, the correct option C.
