The correct option is C is attending
In order to find out the correct form of the verb needed, let's first understand these tenses. Present continuous tense is used to express an action that is continuing at the moment. Usually, in this case, the start time of the action isn't given. Present perfect continuous tense is used to express an action that has started in the past, continuing in the present, and might go on or end in future. Here, usually the start or the end time of the action is given. This sentence says - 'these days'. Since the start or the end time of the action is not given, we can say that present continuous tense is required here. Hence, the correct answer is Option C - 'Bharti is attending yoga classes these days.' Option A is incorrect as it doesn't have an auxiliary verb. Option B is incorrect as 'has' is used in case of perfect tenses. Option D is incorrect, as it's not present continuous tense. Also, for perfect continuous tense, we need 'has been attending' and not 'been attending'.