Sentence completion: the sentence given below has a blank. Choose the modal verb phrase that best completes the sentence. Mr. Sen is absent today. He _____ sick.

Introduction / Context:
This question tests your understanding of modal verbs used to express deduction or logical conclusion about a present situation. Mr. Sen is absent today, and the speaker is trying to guess the reason. The choice of modal verb shows how certain the speaker feels about the explanation.

Given Data / Assumptions:

• Sentence: Mr. Sen is absent today. He _____ sick.
• Options: has to be, could have been, might be, must have been, should have been.
• The first sentence describes a present fact: Mr. Sen is absent today.
• The second sentence offers a probable explanation for this absence.

Concept / Approach:
When we make a strong logical guess about why something has happened, we often use must have plus past participle, as in He must have been sick or He must have forgotten. Here, the absence is already a fact, and the speaker is reasoning backward about what condition earlier in the day led to this absence. Thus the form must have been sick expresses a strong degree of certainty about a past cause of a present absence.

Step-by-Step Solution:
Step 1: Recognise that the speaker is drawing a conclusion about the likely reason for Mr. Sen s absence. Step 2: Recall that must have plus past participle is used for strong logical deductions about the past. Step 3: Fit must have been into the sentence: He must have been sick. Step 4: Check that this expresses a natural, strongly probable explanation of the present fact that he is absent.

Verification / Alternative check:
Consider the other options. Has to be sick would normally be used in He has to be sick to be absent so often, which is about necessity, not deduction about a specific day. Could have been sick suggests a possibility in the past but does not directly explain the current absence as strongly. Might be sick uses present time, but the structure Mr. Sen is absent today. He might be sick is also possible English; however, many exam keys focus on the pattern must have been for a more definite logical conclusion from the observed fact. Should have been sick is incorrect because we do not usually say someone should have been sick as a reason for being absent.

Why Other Options Are Wrong:

• has to be: Expresses obligation or necessity, not a guess about a cause.
• could have been: States only a weak possibility without strongly linking it as the reason for the known absence.
• might be: Uses present reference and is less precise in explaining a known current absence on a specific day.
• should have been: Suggests expectation rather than actual deduction; it would imply that being sick was the correct thing to do, which is not intended.

Common Pitfalls:
Many learners confuse must be with must have been and do not clearly separate deductions about the present from deductions about the past. A useful guideline is: must be for a present continuous situation (He must be working now), and must have been for a past situation that explains a current result (He must have been sick, so he stayed home). Applying this rule helps you choose must have been in this question.

Final Answer:
Correct option: must have been.