可持续发展问题世界首脑会议又简称“地球峰会”，每( )年举行一次。
A．10B．20C．5D．8
参考答案：A
The process of growing up is complex for every person, ________ there are many influential factors in a person's growth as well as the development of his personality.
A．but
B．so
C．for
D．therefore
《安全生产许可证条例》规定，安全生产许可证有效期为()年，不设年检。
A.5
B.1
C.3
D.2
