题干
2011年甘肃平凉市崆峒区“4·7”“投毒牛奶”事件经媒体曝光后引起政府的高度重视。经检测，毒牛奶确由掺入的亚硝酸钠(NaNO2)造成。NaNO2中氮元素的化合价为( )
A：+5
B：+4
C：+3
D：-3
答案(点此获取答案解析）
C
2011年甘肃平凉市崆峒区“4·7”“投毒牛奶”事件经媒体曝光后引起政府的高度重视。经检测，毒牛奶确由掺入的亚硝酸钠(NaNO2)造成。NaNO2中氮元素的化合价为( )
A：+5
B：+4
C：+3
D：-3
It is noon now. The sun is high in the sky. It is very hot. Look at the tree. The shadow is short. 
It is evening now. The sun goes down in the west(西方). Look at the tree, the shadow is long again. 
It is night now. The moon is high in the sky. There are some stars in the sky too. 
