—Do you know the boy ______ is sitting next to Peter?

—Yes. It's Peter's friend. [ ]

A. who

B. which

C. whom

D. /

甲状腺超声检查示内圆形无回声区，边界光滑、整齐，侧方声影内收。应考虑（）

A.甲状腺囊肿

B.甲状性血肿

C.甲状腺癌

D.结节性甲状腺肿

E.单纯性甲状腺肿