—Listen! Helen is singing in the next room.

—It _______ be Helen. She has gone to Beijing.[ ]

A. can't

B. mustn't

C. may

D. should

. ______ is the kindness of the nurse that the patient can never be ______ to her.

A．So; too thankful

B．Such; too thankful

C．So; that thankful

D．Such; thankful such