The correct option to complete the sentence is option B, "Turning." This is the present participle form of the verb "turn," which is used as an adjective to describe the noun "stereo." When used in this way, the present participle form of a verb typically follows the word "mind" and indicates that the speaker is asking the listener to perform an action.

Option A, "Turn," is the base form of the verb "turn," which is used as an imperative verb to instruct the listener to perform an action.

Option C, "To turn," is the infinitive form of the verb "turn," which is used to indicate the purpose or goal of an action.

Option D, "To turns," is incorrect because "turns" is not the correct conjugation of the verb "turn" in the infinitive form.

Option E, "Turned," is the past tense form of the verb "turn," which is used to describe an action that has already been completed.