Topic: verb (ক্রিয়া),

Best Answer Explained in Below-:

The correct option for the sentence "The principal had his teachers --- their lessons in advance." is C) 'Plan'. To understand why, we need to analyze the structure of the phrase "had his teachers." The verb "had" here functions as a causative verb, indicating that the principal is causing or instructing the teachers to take an action regarding their lessons.

In this context, "plan" serves as the base form of the verb, which fits the structure required after "had." The full phrase would read, "The principal had his teachers plan their lessons in advance," suggesting that he instructed or required them to prepare their lessons ahead of time.

The other options do not fit appropriately:
- A) "Being planned" is a gerund phrase that does not function correctly in this context.
- B) "Planned" is a past participle that would imply the lessons were already prepared, which alters the intended meaning.
- D) "Was planning" is a past continuous tense that suggests an ongoing action, rather than a directive from the principal.

Thus, option C) 'Plan' is the correct choice to complete the sentence effectively and meaningfully.