LED是电致发光的固体半导体高亮度点光源，其缺点主要有（）。
A．显色指数低
B．价格昂贵
C．功率低
D．不耐冲击
参考答案：A, B, C
______ that he has no qualifications in business management, Ken plans to gain the necessary skills by taking a part-time course.
A．Concerning
B．Concerned
C．Being concerned
D．To concern
固定义齿修复中，牙齿仍可以选作基牙的倾斜度为（）
A.35°
B.40°
C.30°
D.45°
E.60°
