直角坐标中的累次积分
可化为极坐标先r后θ次序的累次积分I=______.
参考答案:[*]
解析:[*] [*]
Last night I called him. ______ 8:30, but he was not in. [ ]
A. by
B. at
C. in
D. on
《煤矿安全监察条例》体现了国家的意志,反映了业主的利益,是业主意愿的表现。