After visiting China, most of the foreign friends said they would never forget the time _____ they had spent

in China.[ ]

A. what

B. that

C. when

D. at which

甲亢内科治疗停药首选实验室检查是（）

A.FT₃、FT₄

B.TT₃、TT₄

C.TSAb

D.rT₃

E.甲状腺摄¹³¹I率