同学你好，该知识点来自沪江网校《新概念英语1、2、3、4册连读【抢学班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
It is always worrying when sites are opened, because they can get damaged by tourists constantly visiting.It would be terrible if they were ever lost again through damage.
当景点开放时总是令人担忧的，因为它们可能会被不断访问的游客破坏。如果它们因损坏而再次丢失，那就太可怕了。
现在进行时可以表示动作的一种持续性，动作正在发生，且可能持续发生
when后面是表示一个事实描述，用的一般现在时
现在描述的是一种状态：开放会有担忧，什么时候开放不是重点
It would be terrible if they were ever lost again through damage.这是虚拟语气
与现在事实相反的假设：从句:主语+过去时 主句:主语+should/would/could/might+do
祝同学学习愉快~