Fill in the blanks with the correct modal
You ____ an ENT as soon as you _____ this irritating pain

should have visited/felt

The correct modal to fill in the blank is should have visited. The modal should is used to express obligation or necessity, and the past perfect tense had visited is used to describe an action that was completed before another action in the past. In this sentence, the speaker is saying that the person should have visited an ENT as soon as they felt the irritating pain.

The other options are incorrect. The modal could is used to express possibility, but it does not have the same sense of obligation as should. The modal might is also used to express possibility, but it is even more tentative than could. The modal had to is used to express necessity, but it is not used in the past perfect tense.