题干
When leaders of Chinese mainland（大陆）and Taiwan met in Singapore for ________ first time since 1949, President Xi said, "Today will be remembered in _________ history."
A：the; the
B：the; /
C：/; /
D：/; the
答案(点此获取答案解析）
B
结构，而分子式为CnH2nO2 (n≥1) 的羧酸类有b种结构，则a和b的大小关系为
