They're kind of moving around, coming up and under and over.它們只是游來游去，在海平面上上下下

up and down:上上下下； 來回

The lion paced restlessly up and down in its cage.

獅子在籠子里不安地來回走動。

You'd think it'd be quite easy to keep track of a 40-tonne animal.你會以為追蹤四十噸的動物蠻簡單的

keep track:通曉事態(tài), 注意動向

He reads the newspapers to keep track of current events.

他閱讀報紙以了解時事。

We have to keep track of every cent we spend.

我們得記下我們花的每一分錢。

One minute they're there, we get up reasonably close,它們一下子在那里，我們趕緊靠近

get up:變得猛烈；籌備

The wind is getting up.

風(fēng)越刮越大。

We're getting up a party for her birthday.

我們要給她開生日慶祝會。

then they'll come up again and they'll be 300 yards away,可是卻在三百碼的距離之外出現(xiàn)

come up:出現(xiàn)

The flowers are just beginning to come up.

花剛開始長出地面。