Answer:
We <u>must</u> not use mobile phones during exams.
Explanation:
Modal verbs are those verbs that are used to express modality, possibility, ability, likelihood, capability, etc in the sentence. The modal verbs include may, must, can, could, should, etc among others.
In the given sentence, the use of mobile phones in exams seems to be the main theme. So, considering the situation of the event, it is fair to say that the modal verb that will replace the verb form in the sentence is "must". This will ensure that the rule is strict adherence to a fair exam. It also emphasizes the strong sense of the prohibition, having a much stronger effect than the word "should". "Must" gave a definite statement while "should" is a much more lenient statement.
Thus, the appropriate modal verb for the given sentence is "must", making the sentence- <em>"we must not use mobile phones during exams"</em>.
