The correct option to fill the gap in the sentence "If I were the Head of the English Department in my school, I .... make oral English a compulsory subject" is A. would. Step-by-Step Explanation:

1. Understanding the Conditional Structure:
2. The sentence is a conditional statement, specifically a second conditional. This type of conditional is used to talk about hypothetical situations that are unlikely or impossible in the present or future.
3. The structure of a second conditional sentence is: If + past simple, would + base form of the verb.
4. Identifying the Hypothetical Situation:
5. The phrase "If I were the Head of the English Department" indicates a situation that is not currently true (the speaker is not the Head of the English Department).
6. The use of "were" instead of "was" is correct here because in formal English, "were" is used for all subjects in hypothetical situations.
7. Choosing the Correct Modal Verb:
8. The verb that follows "I" in the main clause (after the comma) should express a strong intention or decision regarding the hypothetical situation.
9. The word "would" indicates a strong likelihood or intention to take action if the condition were met. In this case, it suggests that if the speaker were in the position of Head of the English Department, they would definitely make oral English compulsory.

Why the Other Options Are Incorrect:

• B. could:
• "Could" implies ability or possibility. If the sentence said "I could make oral English a compulsory subject," it would suggest that the speaker has the ability to do so, but it does not convey the same level of intention or decision as "would." It leaves the action more open-ended and less definitive.
• C. should:
• "Should" implies a recommendation or obligation. Saying "I should make oral English a compulsory subject" suggests that it is the right thing to do, but it does not express the speaker's intention to take that action. It sounds more like advice rather than a commitment.
• D. might:
• "Might" indicates a possibility but lacks certainty. If the sentence were "I might make oral English a compulsory subject," it would suggest that there is a chance the speaker could do it, but it is not certain. This option is too weak for the context of making a definitive decision.

Summary of Key Points:

• The correct answer is A. would because it expresses a strong intention in a hypothetical situation.
• The second conditional structure is used to discuss unlikely or impossible situations.
• "Could," "should," and "might" do not convey the same level of commitment or intention as "would."
• Understanding the nuances of modal verbs is crucial for choosing the appropriate option in conditional sentences.

Revision Summary:

• Use "would" in second conditional sentences to express strong intentions.
• "Could" indicates ability, "should" suggests obligation, and "might" implies possibility.
• The structure of second conditional: If + past simple, would + base form of the verb.
• Always consider the context to choose the most appropriate modal verb.