短语讲解：
1. This, as the United Nations faces a lawsuit for alleged unsanitary conditions at a U.N. base that may have introduced cholera into Haiti.
introduce into引进; 插入
例句：Tea was introduced into Europe from Asia.
茶叶是从亚洲传入欧洲的。
2. She walked and rode motorcycles for six hours to arrive at this cholera treatment center.
arrive at到达, 来到
例句：One day a letter from my father arrived at the school.
有一天, 学校收到了我父亲的一封信。
3. And a U.N. panel of experts has traced it back to Nepalese peacekeepers at this U.N. base.
trace back to追溯到…
例句：The rumor has been traced back to a bad man.
那谣言经追查是个坏人造的。
4. So, meantime, the centers train Haitians to treat drinking water with chlorine tablets and to practice good hygiene.
treat with用防护措施处理某物
例句：We first treated the wood with creosote.
我们先用杂酚油对木柴进行加工。
5. She will leave in a couple days to return to her home high up in these mountains.
return to返回到…
例句：News of the astronauts' safe return to earth was delayed.
宇航员安全返回地球的消息被推迟。
