Your usual teacher has lost his voice and______I am taking his place today.

A．nevertheless

B．however

C．moreover

D．accordingly

所谓防护性能好的屏蔽材料是指()

A．对X线吸收能力强，散射量多

B．对X线吸收能力弱，散射量少

C．只考虑对X线的吸收能力强

D．只考虑材料产生的散射量少

E．对X线吸收能力强，而散射量少