A:①②
B:①③
C:②④
D:②③
①N2 ②Mg2+ ③SO2 ④ ⑤
—Come on, Sandy. Everybody will be lucky or ____(成功的) sometime in their life.
—Thanks, I'll try again.
“天苍苍,夜茫茫,风吹草低见牛羊”的景观是指( )