This question tests your understanding of modal expressions used for giving advice or expressing necessity. Let's analyze the conversation:

Context: Person A asks if Priya apologized after an argument. Person B says "No, but she ________ do that soon."

Step 1: Understand the meaning needed - Person B is suggesting that Priya should or needs to apologize soon, implying advice or necessity.

Step 2: Evaluate the options:

• "Should rather" - Incorrect combination. "Should" alone expresses advice, but "rather" doesn't fit here.
• "Had better" - Correct. This expression means "ought to" or "should" and is used for strong advice or warning about future consequences.
• "Better had to" - Incorrect word order. The proper form is "had better," not "better had."
• "Would rather" - Incorrect. This means "prefer to" and is used for expressing preferences, not advice or necessity.

Step 3: The correct answer is "had better" because it perfectly fits the context of giving strong advice about what Priya should do soon.

Final Answer: The blank should be filled with "had better" - "No, but she had better do that soon."

Related Concepts

Modal Expressions: These are special verb phrases that express necessity, advice, permission, or possibility. Common examples include:

• Should - for advice
• Had better - for strong advice with implied consequences
• Would rather - for preferences
• Must - for necessity or obligation

Usage Rules

Had better: Always followed by base form of verb (without "to"). Structure: Subject + had better + base verb

Example: "You had better finish your homework before going out."