It was commanded that the coal mine survivors ____ to the nearest hospital for treatment.
A:must send
B:be sent
C:would be sent
D:should send
施行人工降雨时,是飞机在云层里撒干冰,干冰迅速____而吸热,使云层中水蒸气急剧遇冷而____成小冰晶,小冰晶逐渐变大,在下落过程中又____成小水滴落下来.(填物态变化名称)
下列说法正确的是()
已知圆C1:(x+3)2+(y+4)2=4
(1)求与圆C1关于原点对称的圆C2的方程;
(2)求圆C1与圆C2的外公切线的方程.
我国各民族的分布特点是( )