They got a terrible shock when they found that the hole was closed.

当他们发现洞被堵住时，他们大吃一惊。

From the 1940s through the 1970s, the trees closed the tiny holes in their leaves known as stomata to protect themselves from acid rain.

从上世纪40年代到70年代，红杉树关闭了叶子上的小孔来保护自己免受酸雨侵袭。