题干
First impressions are the most lasting. After all, you never get _____ second chance to make ______ first impression.
A：a; the
B：the; the
C：a; a
D：the; a
答案(点此获取答案解析）
C
2Z(g)，已知X2、Y2、Z的起始浓度分别为0.1mol/L、0.3mol/L、0.2mol/L，在一定条件下，当反应达到平衡时，各物质的浓度有可能是
