Mary . . . . . . . . seats for us.

Solution (By Examveda Team)

Definition:
The sentence suggests a recommendation or duty regarding saving seats. The correct verb choice should indicate an obligation or advisability. Both "ought to" and "should" are modal verbs used to express advice or recommendations. Correct Answer:
The correct option is Option B: should save. Explanation:
- "Should" is a modal verb used to give advice, make recommendations, or express duty.
- In this sentence, "should save" means that it is advisable or expected for Mary to save seats for us.
- The correct sentence is: Mary should save seats for us.
Why Other Options Are Incorrect:
- Option A: ought to save → Although "ought to" is similar to "should," it is less commonly used in modern English and sounds slightly more formal.
- Option C: would have saved → Incorrect because "would have saved" is in the past perfect conditional, which is used when referring to something that did not actually happen in the past.
- Option D: would save → Incorrect because "would save" is used in conditional sentences, often depending on another action (e.g., "Mary would save seats if she arrived early").
Final Answer: Option B: should save.