Explanation
The correct option to complete the sentence is:
A) is
Explanation: The correct sentence would be "Gymnastics is becoming popular." In this sentence, "gymnastics" is the subject, and since it is a singular noun, the verb "is" should be used. Option B) are (the plural form of the verb "to be") is not appropriate in this context since "gymnastics" is a singular noun. Option C) were (past tense of the verb "to be") and Option D) have been (present perfect tense of the verb "to be") do not fit the sentence structure or convey the correct meaning.
