The correct option to put in the option provided is;
None of the verbs provided will improve the meaning of this sentence. We can confirm this by trying out all the options provided thus:
1. Their sound is being level, precise, and flawless. (This sentence is wrong because of the incorrect usage of the verb, is)
2. Their sound is being being level, precise, and flawless. (This sentence is also incorrect because of the redundancy in the use of the word, being)
3. Their sound are being level, precise, and flawless. (The verb used here is also inappropriate)
The correct wording of this sentence should be: "Their sound is level, precise, and flawless".
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https://brainly.com/question/2277858