光泽是指宝石表面对光的反射能力，宝石中最多见的光泽为（）
A、油脂光泽
B、丝绢光泽
C、蜡状光泽
D、玻璃光泽
参考答案：D
Sam ______ some knowledge of the computer just by watching others working on it.
A．brought up
B．looked up
C．picked up
D．set up
