The answer is variant C because it isolate an appositive developed phrase from the remained sentence.
C. My only pet, which is a ball python, sleeps during the day.
Option C is the correct answer because it properly uses commas to separate the non-essential clause that describes the pet. The other options contain punctuation errors that need correction. Hence, the accurate sentence is: 'My only pet, which is a ball python, sleeps during the day.'
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