With the quality-oriented education (素质教育) being carried out, teachers won't too much importance to students' grades.
A：involve
B：attach
C：display
D：stress
12=1
12﹣22=﹣3
12﹣22+32=6
12﹣22+32﹣42=﹣10
…
照此规律，第n个等式可为____．
影响城市空气质量的因素是（ ）
