题目

 ____ each other for years, they talked almost the whole night and had a wonderful time. A. Not having seen      B. Having not seen     C. Not seen       D. Not to see 答案：A近年来，我国许多城市禁止使用含铅汽油，其主要原因是 [　　] A．提高汽油的燃烧效率B．降低汽油成本 C．避免铅污染大气D．铅资源缺乏