下列每组物质发生所述变化克服的作用属于同种类型的是（ ）
A．氯化铝和干冰升华
B．钠和硫熔化
C．食盐和氯化氢溶解于水
D．二氧化硅和二氧化硫熔化
答案：A
— Where are the guests to be from tomorrow?
— Many an American boy and many a British girl as well as the teachers ________ to be present. [ ]
A. have been invited
B. has been invited
C. were invited
D. was invited
说出：V-3工作原理？
