常温下pH＝3的二元弱酸H2R溶液与a L pH＝11的NaOH溶液混合后，混合液的pH刚好等于7（假设反应前后体积不变），则对反应后混合液的叙述正确的是A. c(R2－)
There are ____ of students in the school, but only ____of them are girls. A. hundreds, two hundred B. hundred ,two hundreds C. hundreds, two hundreds
下列属于新中国教育方针和政策的重要内容的是 ( ) A. 成立“红卫兵”组织 B. 知识青年“上山下乡” C. 培养有社会主义觉悟的有文化的劳动者 D.
1. She____much younger than she really is. A.turns B.becomes C.grows D.appears
世界上面积最大的平原是（ ） A．东欧平原 B．华北平原 C．亚马孙平原 D．西西伯利亚平原
Fred is always ________ because he often does something good for his health outdoors. A. weak B. nervous C. serious D. energetic
With your workload growing, you may be telling yourself a vacation is one luxury (奢侈) you can't afford. But the truth is that you can't afford not to take one. A vacation allows you the opportunit
The drink is_________ delicious________ everyone in the room enjoys it.A. such...that B. too...to C. so...that
过圆
的圆心, 则
的最小值为( ) 