急急急)Oliver. used to ___thin,but he has put on a lot of weight. (A)have been (B)had been (C)being (D)be?

Oliver, who has put on a lot of weight,
-----adjective clause after a noun,
(D) used to be thin
-------another adj phrase after the noun "Oliver" by function.
which means
Oliver being thin puts on weight.
when(C) "being thin" is placed after the noun "Oliver".Hence (D) is correct.

used to +原V

表示過去常常做某事(但現在沒有)