1.Choosing what to eat is no longer as easy as it once was.
[答]作连词，表示比较。又如：My hometown is no longer the same as it was.我的家乡同过去不一样了。
2.if we want to keep up with the high pace of modern life,we had better learn to make the right choices about what and how we eat.如果我们要跟上现代生活的步伐，我们最好学会正确的选择吃什么以及怎么吃。
[答]这里if引导的是条件状语从句，we had better...是主句，what and how we eat是宾语从句做about的宾语。keep up with赶上，跟上，had better最好。
3.When we choose what to buy and eat,we had better think if the food will give us the nutrients we need.当我们选择我们想要买和想要吃东西的时候，我们最好想一想这些食物是否提供了我们所需要的营养。
4.Some nutrients help build our body and amke it stronger.一些食物有助于我们增强体魄。
[问]build our body and make it stronger一起做help的宾语吗?
5.Caicium,which is found in eggs,milk and other dairy products,is good for our bones and teeth.
[问]which is found in eggs,milk and other dairy product是定语从句吗?
6.Other nutrients help keep our body functioning well.其他的营养物有助于我们的身体正常运转。
7.But the choices we make are not just about nutrion.但是，我们做出的选择不仅是营养方面的。
8.Eating habits become part of who we are:people become vegetarians either because they believe it is healthier not to eat meat or because they so not think we should kill animals for food.
[答]主句是：Eating habits become part of who we are.Eather...,or...引导两个because原因状语从句。
9.We also make choices based on how the products are grown or made:environmentally friendly foods,or"eco-foods",are made by companies who have tried to use green and clean ways to make the foods.我们对产品的作出的选择还决定于生产和加工方式，要是环保性的或者说是生态性的食物，是厂家用绿色而又清洁的方式生产出来的食物。
[答]对。that are grown without chemicals做vegetables的定语;that can be harmful to human beings and the environment做chemicals的定语。
1.Nobody knew that it was going to be different from other planets going to be different from other planets going round the sun.
going round the sun为现在分词短语定语，表示一般的动作。Eg:Men breaking the law will be punished.现在分词短语，也可表示进行的动作
2.Weather life will continue on the earth for millions of years to come will depend on whether this problem can be solved.
for millions of years to come中不定式to come作定语，与前面的名词有逻辑上的主谓关系。
Eg:She is the last person to tell lies.
3.The problem was that the earth became violent because it was not clear whether the solid shape was to last or not.
The problem was that…,that引导表语从句，that只起连接作用，无意义，但不能省略。Eg:The trouble is that we are short of money.
4.As the earth cooled down,water began to appear on its surface.
as conj.随着，在…期间;由于，因为;尽管，即使;当…的时候;像…一样5.That made it possible for life to begin to develop.
it是形式主语，真正的主语是不定式to begin to develop.Eg:He thinks it’s his duty to help others.