Father said, “Do not waste time.”

The correct answer is A: Father advised not to waste time. This question tests your ability to convert direct imperatives (commands or advice) into reported (indirect) speech. When reporting commands, requests, or advice, the structure typically involves a reporting verb followed by an infinitive phrase.

• The reporting verb "said" is replaced by a more specific verb that conveys the nature of the imperative, such as "advised," "ordered," "told," "requested," or "warned." In this context, "advised" is the most appropriate choice, as it implies a helpful suggestion rather than a strict command.
• For negative imperatives (starting with "Do not..."), the structure in reported speech becomes not + to + infinitive. So, "Do not waste time" transforms into "not to waste time."
• There is no conjunction like "that" used with this structure.

Options B, C, and D are incorrect because they either retain the direct speech structure, use an inappropriate reporting verb, or fail to correctly form the negative infinitive phrase. Therefore, "Father advised not to waste time" is the grammatically correct reported form of the imperative.