In the sentence "I did not feel like going out yesterday, but on account of my son's illness I had to go to the doctor.", the underlined modal phrase must be checked. Choose the option that best improves this phrase, or select no improvement if the sentence is already correct.

Introduction / Context:
This sentence improvement question looks at the correct modal expression of necessity in the past. The speaker talks about not wanting to go out on a particular day, but still going to the doctor because of a child's illness. The phrase had to go expresses an obligation or necessity that existed yesterday. You must decide whether this expression is correct or whether one of the alternatives would better convey the intended meaning.

Given Data / Assumptions:

• Sentence: I did not feel like going out yesterday, but on account of my son's illness I had to go to the doctor.
• The underlined part is had to go to the doctor.
• Options: have, might have, ought, no improvement.
• The context is a past situation where the speaker was compelled by circumstances to visit a doctor.

Concept / Approach:
In English, the modal verb must does not have a direct past form, so we use had to to express past necessity or obligation. The structure had to plus base verb is therefore the standard way to say that something was necessary in the past. In contrast, have by itself suggests present obligation, might have suggests possibility in the past, and ought without to is incomplete. Since the necessity existed yesterday, had to go is the correct expression and needs no improvement.

Step-by-Step Solution:
Step 1: Identify the time reference: yesterday, which clearly places the action in the past. Step 2: Note the contrast between did not feel like going out and the fact that the speaker still went to the doctor because of illness, which implies a strong necessity. Step 3: Recall that past necessity is expressed by had to, as in I had to visit the doctor, He had to work late, They had to cancel the trip. Step 4: Evaluate the original phrase had to go to the doctor, which correctly combines past necessity with the action of going. Step 5: Examine option A, have, which would give I have to go, a present tense structure that conflicts with yesterday. Step 6: Examine option B, might have, which expresses a past possibility or unrealised action, not a completed necessary action. Step 7: Examine option C, ought, which is incomplete without to and in any case expresses duty more than actual necessity in the past.

Verification / Alternative check:
Compare the sentence with similar statements: I did not want to drive, but I had to because there were no buses, She did not feel well, but she had to attend the meeting. In each case, had to indicates that circumstances forced an action, even though the person did not wish to do it. Replacing had to with have, might have, or ought in these examples would either change the tense or weaken the sense of obligation. The same pattern fits perfectly in the exam sentence with the doctor visit.

Why Other Options Are Wrong:
Have does not match the past adverb yesterday, so it would create a tense mismatch. Might have would give a sense that going to the doctor was only a possibility or that it perhaps happened, which does not match the clear statement that the speaker went. Ought, without to and without a clear auxiliary structure, is incomplete and cannot stand as a replacement for had to go.

Common Pitfalls:
Some candidates may overthink the presence of had and assume it must be replaced, forgetting that had to is exactly how English expresses past obligation. It is important to distinguish between correcting real errors and changing correct structures unnecessarily. Whenever you see an obligation tied to a completed past event, such as yesterday or last week, check whether had to is already in place before selecting another option.

Final Answer:
The phrase is already accurate, so the correct choice is no improvement.