My classmates were playing happily _____ I got to the park. [ ]
A. when
B. before
C. after
A
冬期施工一般现浇混凝土结构宜优先选用()水泥。
A.普通
B.矿渣
C.火山灰
D.粉煤灰
杆上变压器及变压器台架安装有什么要求?