仪器和设备按照传染的风险等级分为（）类。
A.1
B.2
C.3
D.4
E.5
参考答案：C
—Where's my music disc? I can't see it!
—You'd better ________ the disc carefully in your bedroom. [ ]
A. look up
B. look through
C. look for
教师讲课声音抑扬顿挫是为了引起学生的（ ）注意。
A．无意
B．有意
C．有意后
D．随意
