小儿肺炎引起全身各系统病理生理变化的关键是（）
A.病原体侵入
B.缺氧
C.二氧化碳潴留
D.毒素作用
E.酸中毒
参考答案：B
（9分）在反应3Cu+8HNO3(稀)=3Cu(NO3)2+2NO↑+4H2O中，有19.2gCu被氧化，则被还原的HNO3的质量为多少？
Among the 15-year-old children, some ____ studying in university while others are still learning to read and
write. [ ]
A. should have been
B. would have been
C. can be
D. must be
