.Let’s _______(jump) into the water and have a swim.jump 理由?Let’s _______(jump) into the water and have a swim.

.Let’s _______(jump) into the water and have a swim.jump 理由?Let’s _______(jump) into the water and have a swim.
.Let’s _______(jump) into the water and have a swim.jump 理由?
Let’s _______(jump) into the water and have a swim.

.Let’s _______(jump) into the water and have a swim.jump 理由?Let’s _______(jump) into the water and have a swim.
Let’s jump into the water and have a swim.这里就填jump.
因为Let's是Let us的缩写,我们通常把Let's看做祈使句的开头,当我们要求别人怎么做时,我们可以用提建议的语气,Eg:“Let's play game/Let's watch TV.”一样的道理.这是一个句型短语,“Let's+do(动词原形)”.同样我们可以把它看作let的句型.例如“let sb/sth do”.
还有什么问题也可以问我,不过可不可以加点悬赏,我在愁财富值!

Jump
这个结构就跟let's go这样的搭配一样。

jumping：因为let's引导现在进行时

let's do sth