Fill in the blanks with the correct modal
Tom is not here. Then he _____ be working in the garden.

must

 The correct answer is OPTION 4 - "must"

The sentence "Tom is not here. Then he _____ be working in the garden." suggests a strong logical conclusion based on evidence.

• "Might" → Expresses possibility but with uncertainty. (Not the best fit here.)

• "Will" → Expresses future certainty, but this sentence is about a present assumption.

• "Should" → Expresses obligation or expectation, not logical deduction.

• "Must" → Expresses a strong logical deduction based on the given situation.

Thus, the correct sentence is:
"Tom is not here. Then he must be working in the garden."