{#blank#}1{#/blank#}表示"当……时候"，既指时间点，又指一段时间，when 引导的时间状语从句中的动词可以是终止性的也可以是延续性的。

When the teacher came in, the students were talking.

When she arrives, I'll call you.

{#blank#}2{#/blank#}表示"当……时候"，仅指一段时间，从句中的动作必须是延续性的，一般强调主从句的动作同时发生， while还可以作并列连词，意为"而、却"，表示对比关系。

Lisa was singing while her mother was playing the piano.

Tom is strong while his younger brother is week.

    Have you ever been to the Dead Sea? People all over the world {#blank#}1{#/blank#}(花费) thousands of dollars traveling there every year. It is {#blank#}2{#/blank#}(著名的) for being lifeless. But now its name may need to be changed, because scientists have {#blank#}3{#/blank#}(发现) there is fresh water from the bottom.

    The Dead Sea is on the border(边境) of Jordan to the {#blank#}4{#/blank#}(东边) and Israel to the west. There is a lot of salt in the sea water. What will you do if you have a {#blank#}5{#/blank#}(机会) to travel there? Will you swim in the Dead Sea? When you swim in it, you won't fall {#blank#}6{#/blank#}(向下) to the bottom. For this reason, more people feel {#blank#}7{#/blank#}(放松的) to stay here for their holidays.

    In the Dead Sea, {#blank#}8{#/blank#}(无论什么) you want to do, you don't have to worry about your {#blank#}9{#/blank#}(安全). Even though you can't swim, you can play games with your friends on the water, and also {#blank#}10{#/blank#}(享受) sunshine, sand and the views of the sea.