基站天线应处于避雷针()保护角内,保护角是指避雷针顶部至()和()。
参考答案:45度;天线顶部;避雷针的夹角
— I am ________ endless examinations.
— Cheer up, David.Keep on until the college entrance examination ends. [ ]
A. caught up with
B. come up with
C. fed up with
D. put up with
桥梁按其结构受力不同可分为三类,下列不属于该分类的是()。
A、石桥
B、梁桥
C、拱桥
D、斜拉桥