VOA慢速英语:Sleeping and Dreaming of Comets

短语讲解：

1. Whereas when during sleep, really work very, very hard on removing all the waste that builds up when we are awake.

build up 逐步建立；增进
例句：It is triggered when electrical charges build up in storm clouds.
电荷在积雨云中聚积起来就会触发闪电。

2. Doctor Nedergaard says the next step is to find out if the human brain has a similar cleaning system.

find out 查明,发现
例句：Find out what makes you happy.
找出什么能让你快乐。

3. Because a comet is this dirty snowball of not only rock, but  rock mixed with ice.

not only...but... 不但…而且
例句：But turbulence produces not only risks but also opportunities.
但波动带来的不仅是风险，还有机遇。

4. He says no one has seen a comet hit and lived to tell about it.

tell about 谈及；讲述
例句：We will tell about the effects of that decision next week.
下周，我们将向你讲述这一决定所带来的影响。

5. She tells reporter Tom Banse not to worry as he prepares for his turn.

prepare for （使）为…作准备；（使）对…有思想准备
例句：Now is the time to prepare for the worst.
现在就应该为最坏的状况做准备。

6. The large saltwater tank holds 17 sharks of six different species, and a number of smaller fish.

a number of 许多的；一些
例句：A number of people are studying english nowadays.
当今社会有很多人在学习英语。