重点讲解：
1. be surrounded by
围绕；环绕；
eg. It's also called oriental venice and surrounded by water.
古镇被绿水围绕，因此也享有东方威尼斯的美誉。
eg. The sheep were surrounded by stockade.
羊被栅栏圈着。
2. keep out
不许入内； 阻止；
eg. She stamped her feet on the pavement to keep out the cold.
她在人行道上跺着双脚取暖。
eg. They sandbagged their homes to keep out floods.
他们在房屋周围堆沙袋以抵御洪水的侵袭。
3. keep sb. from sth.
阻止（或防止、阻碍）…做；
eg. He slides the bolt in place to keep the door from swinging.
他推上插销，使门不摇晃。
eg. I tucked some plastic wrap around the sandwiches to keep them from getting stale.
我用塑料包装纸把三明治裹起来，防止变质。