环境保护的主要内容是预防和治理由生产和生活活动所引起的环境污染；（）；保护有特殊价值的自然环境；其他
参考答案：防止由建设和开发活动引起的环境破坏
From the dates _________ on the gold coin, we decided that it was made five hundred years ago.
A．marking
B．marked
C．to be marked
D．having been marked
______no friction between the surface of the road and our feet, we could not walk at all.
A．If there was B．Were there C．Was there D．There was
