Select the correct indirect speech form of the given sentence.

The teacher said, "You must work hard for your exams."

The teacher advised her students to work hard for their exams.

The correct indirect speech form of the given sentence is:

The teacher advised her students to work hard for their exams.

The other options are incorrect because they do not follow these rules:

• The teacher was advising her students to do work hard for their exams. - This sentence repeats the word "to" twice, which is grammatically incorrect.
• The teacher told students for working hard for their exams. - This sentence does not change the imperative mood to the infinitive mood.
• The teacher was telling her students to work hard for their exams. - This sentence uses the present continuous tense for the reporting verb, which is incorrect in indirect speech.