题干
We urge ________ extreme caution in ________ use of this medicine, which has not been officially approved yet.
A：an; the
B：an; 不填
C：不填; the
D：不填; 不填
答案(点此获取答案解析）
C
，
C2H4(g)在降低温度时平衡向右移动，则下列两个反应： C(s)＋1/2H2(g)