题干
Witnesses said the security forces use tear gas to ________ protests(抗议) by about 200 people in Teheran, although this can't be independently confirmed.
A：break out
B：break down
C：break up
D：break through
答案(点此获取答案解析）
C
NO(g) + SO3(g)在一定条件下建立平衡，再加入一定量的O2，下列说法正确的是 （ ）