Fill in the blanks with the most appropriate option:-

The students _______ a good time in class today.

are having

The most appropriate option to fill in the blanks is are having.

The sentence "The students are having a good time in class today" is in the present continuous tense, which is used to describe an action that is happening now. The other options are not as appropriate.

• Have is the present perfect tense of the verb "to have". This does not make sense in the context of the sentence, as the students are still having a good time in class now.
• Will having is not a grammatically correct sentence.
• Has is the present perfect tense of the verb "to have". This does not make sense in the context of the sentence, as the students are still having a good time in class now, not have had a good time in class.