4. They must study hard to get good marks.

Must they study hard to get good marks?

What must they study hard to get good marks?

Which must they study hard to get good marks?

Where must they study hard to get good marks?

From where must they study hard to get good marks?

Why must they study hard to get good marks?

When must they study hard to get good marks?

How many must they study hard to get good marks?

How many times must they study hard to get good marks?

At what time must they study hard to get good marks?

How much must they study hard to get good marks?

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