Option D is the correct answer. Following the indirect mode of narration, the syntax and tense of the statement is compatible with the first part of the sentence. The question word is followed by the noun and then the verb. The reported verb is also in the past tense. Options A ,B and C do not follow the same syntax. Here, the verb precedes the noun, which is the normal syntax of an interrogative sentence. Moreover, the present tense of the reported verb in options A and C make them incorrect. Therefore, option D is the most appropriate answer.