显成本（Explicit costs）
参考答案：
显成本是指账目上所包括的厂商的正常费用，诸如工资成本和原材料支付。
The two boys_____ games on the computer for three hours, and they would continue till midnight
A．were playing
B．had played
C．had been playing
D．has been chatting
肩关节周围炎主要症状不包括（）
A.肩关节疼痛
B.关节活动障碍
C.夜间疼痛为著
D.病程长者三角肌萎缩
E.肩关节疼痛进行性加重
