The correct answer is C. is sleeping.
The sentence “Don’t make a noise, she is sleeping” is in the present continuous tense. This tense is used to talk about actions that are happening right now. In this case, the speaker is telling the listener not to make a noise because the person they are talking about is sleeping.
The other options are incorrect because they do not agree with the tense of the sentence. Option A, “sleep”, is in the simple present tense. This tense is used to talk about general truths or habits. Option B, “will sleep”, is in the future tense. This tense is used to talk about actions that will happen in the future. Option D, “none”, is not a grammatically correct sentence.
In conclusion, the correct answer to the question “Don’t make a noise, she . . . . . . . ..” is C. is sleeping.