An action in a sentence can be represented in two ways, namely active and passive voice.
The passive voice always uses the past participle form of the main verb irrespective of any tense. Only the auxiliary verbs depend upon the sentence given in the active voice.
The correct answer is C)A lovely song is sung by Srishti.
The option C is correct as the subject of the given sentence (Shrishti) comes in the place of the object (a lovely song) and vice versa and the transformed sentence is also in the simple present tense as the past participle form of the main verb is used (sung) with the appropriate helping verb (was).
Options A, B, and D are wrong as the given sentence is neither in the past perfect tense, nor it is in the simple past tense, and the past participle form of the main verb (sing) is not used respectively.