体内的“宏量矿物质”不包括（）
A.钠
B.钾
C.钙
D.铁
E.镁
参考答案：D
解析：铁是人体必需的微量元素之一，不属于宏量矿物质。
—Maths isn't as as Chinese.
—I agree with you. I think Chinese is than any other subject. [ ]
A. easy, easier
B. easier, easier
C. easy, easiest
D. hard, the most difficult
当采用熔接方式连接光缆时，单芯光纤熔接点衰减平均值应不大于（）芯。
A、0.15DB
B、0.1DB
C、0.2DB
D、0.25DB
