夜床服务通常在晚上（）以后开始，或者按服务台的要求进行。
A.5时
B.6时
C.7时
D.8时
参考答案：B
—Tony, you must have noticed the student who broke the glass.
—I'm sorry.I________attentively.
A．studied
B．was studying
C．am studying
D．would study
正常状态下结晶器保护渣的熔融层厚度应在6-8mm范围内。
