4 now that： 既然，由于
Now that you have come you may as well stay. 既然你来了还是待着吧。
Now that oil is scarce， the fate of the motorcar is uncertain.
由于石油短缺，汽车将来的命运如何就难以预料了。
to leave …alone： 不管，不理；听其自然
Leave me alone - take your hand off my arm. 别动我 - 松开我的胳膊。
I should leave that question alone if I were you. 如果我是你的话，我不会去碰这个问题。
out of step： 步伐不一致，不协调
That boy was out of step during most of the parade.
在游行检阅的大部分时间里，那个男孩的步伐都与别人的不合拍。
I‘m not good at dancing - I always get hopelessly out of step.
我不善长跳舞-总是踩不上点，已经无可救药了。
He is out of step with modern life. 他同现代生活不合拍。
课文精讲：
Jet Lag： Prevention and Cure
The problem of Jet Lag is one every international traveler comes across at some time.⑴ But do you have to suffer？ Understand what it is， and how a careful diet can minimize its worst effects， and your flights will be less stressful. ⑵
1.此句中 “one” 代替前面出现过的 “problem” ， every international traveler comes across at some time 是定语从句修饰one， 省略了关系词that 或which. to come across 意思是 “遇到，碰到”
全句意思：喷气飞机时差综合症是每个乘坐国际航班旅行的人在某个时候会碰到的问题。
2.Understand what it is…这是个祈使句，相当于一个条件状语从句：If you understand what it is…
例句：Work hard and you‘ll succeed. 相当于 If you work hard， you’ll succeed.
The effects of rapid travel on the body are actually far more disturbing than we realize.⑶Jet Lag is not a psychological consequence of having to readjust to a different time zone. It is due to changes in the body‘s physiological regulatory mechanisms， specifically the hormonal systems， in a different environment.
3.此句是个比较结构。disturbing 是分词式的形容词，比较级是more disturbing，far 用来修饰比较级。
此句意思：乘飞机旅行对身体的影响实际上远比我们意识到的更令人焦灼不安。
Confused？ So was John Foster Dulles， the American Secretary of State， when he flew to Egypt to conduct negotiations on the Aswan Dam ⑷He later blamed his poor judgment on Jet Lag.
4.此句中confused 的完整表达是 “Are you confused？” 后一句用了倒装语序，so 位于句首，表示前面所说的情况也适合于本句。Blame…on…把过失归咎于
此句意思：是不是被弄糊涂啦？美国国务卿约翰·福斯特·杜勒斯从美国飞往埃及谈判阿斯旺水坝问题时就被弄糊涂了。他后来把自己在谈判中判断失误归咎于时差综合症。
The effects can be used to advantage， too. President Johnson once conducted an important meeting in Guam and kept the entire proceedings at Washington DC time. The White House working personnel were as fresh as paint， while the locals， in this case， were jet-lagged.⑸Essentially， they had been instantaneously transported to America.
5.该句是由 while 连接的两个并列句，表示前后对比。in this case 作状语，译为“在这种情况下，” the locals 是指关岛的本地人，作主语。
Now that we understand what Jet Lag is， we can go some way to overcoming it.⑹ A great number of the body‘s events are scheduled to occur at a certain time of day. Naturally these have to be regulated， and there are two regulatory systems which interact.
6.now that we understand what Jet Lag is， 原因状语从句中有一个what引导的宾语从句，意为“既然我们了解了时差综合症是什么”。
One timing system comes from the evidence of our senses and stomachs， and the periodicity we experience when living in a particular time zone.⑺ The other belongs in our internal clocks （the major one of which may be physically located in a part of the brain called the suprachiasmatic nucleus） which， left alone， would tie the body to a 25 hour - yes， 25 - rhythm.⑻ Normally the two timers are in step， and the external cues tend to regularise the internal clocks to the more convenient 24 hour period.
7.该句主干结构是“one timing system comes from…。”； from 有两个宾语，由and 连接。
此句意思：一个定时系统来自我们的感官和胃肠饥饿感以及我们在某个特定时区所经受的周期性变化
8.该句的主干结构“The other belongs in our internal clocks …”，which 引导定语从句修饰our internal clocks.在定语从句中，left alone 是过去分词词组作条件状语，相当于条件状语从句If it is left alone.括号中的定语从句也修饰our internal clocks.
此句意思：另一个定时系统在我们的体内时钟内（其中一个主要时钟可能位于我们大脑的称为超交叉核的那部分中）这些体内时钟在不受干扰时，会使人体有一个25小时——是的，25小时——的生理节奏。
If， however， you move the whole body to a time zone which is four hours different， the two clocks will be out of step， like two alarm clocks which are normally set together， but which have been reset a few hours apart. ⑼ Whereas the two clocks would normally sound their alarms together， now they ring at different times. （10）Similarly， the body can be set for evening while the sun is rising.