The correct option is
D Sent, was
NOTE: As the speaker already knows that the t-shirt is of the wrong size, we can understand that the action was completed in the past. Hence, we will use the simple past tense to fill in the blanks.
Option A - 'Sent' is the past form of the verb 'send', but 'was being' is used to define the sentence in the past continuous tense. Thus option A is incorrect.
Option B - 'Was being, was sending' are both used to define the sentence in the past continuous tense. Hence, option B is incorrect.
Option D - 'Was' is the past form of 'be verb'. However, 'was sending' is used to define the action in the past continuous tense. Hence, option D is incorrect.
Option C - 'Sent' is the past form of the verb 'send' and 'was' is the past form of the 'be verb'. As both the verbs represent the sentence in the simple past tense, we can use 'sent, was' here. Hence, option C is the correct answer.
'My uncle, who lives in New York sent me a T-shirt but it was of the wrong size.'