防治水工作必须坚持的原则是什么?
参考答案:
预测预报、有疑必探、先探后掘、先治后采
-Where is Peter?
-He volleyball with his friends in the school gym. [ ]
A. plays
B. played
C.is playing
右图是甲.乙两种物质的溶解度曲线,请依据该图判断下列说法正确的是
A.30℃时,在50g水中最多能溶解30g甲物质
B.将20℃的100g乙物质的饱和溶液升温到30℃,不考虑水份蒸发,该溶液溶质的质量分数将变大
C.30℃时,甲溶液中所含的溶质比乙溶液多
D.20℃时,甲.乙两物质的饱和溶液的溶质质量分数相等