17. Our attention was drawn to the eight-year-old girl who was _______ perfectly at the piano.

A．acting

B．behaving

C．performing

D．doing

NaHCO₃和NaOH的混合物40 g置于密闭容器中充分加热后，排出气体，冷却，混合物质量为38.2 g，则原混合物中NaHCO₃的质量为（   ）

A．1.8 g

B．8.4 g

C．31.6 g

D．38.2 g