7．Choosing what to eat is no longer as easy as it once was.

What to do是疑问词+不定式的结构，在句中作宾语，另外这一结构也可作主语、表语、定语等。如：

①what to do next hasn't been decided yet.（主语）

②I don't know whether to answer it.（宾语）

③The question is how to put it into practice.（表语）

④They exchanged views on the question of whom to elect. （介词宾语）

⑤The key with which to open the door has been lost. （定语）

8．Our eating habits have changed, as has our way of life, and the fuel we need for our bodies is also different.

as在句中引起方式状语从句，此处采用了省略形式，并且是倒装结构，若改用正常语序则为as our way of life has changed。

　as引起的方式状语从句中一般采用正常语序，但在正式语体中，也可采用倒装语序。如：

She plays the piano, as does her mother.

She looks forward, as does her secretary, to the completion of the building.

9．Traditional diets often have too much fat and too many calories for the 21st century person.

　①too much与too many的区别

too much可以作形容词，修饰不可数名词，也可用作副词，修饰动词。例如：

There is too much rain here in spring. She talked too much at the meeting.

too many可作形容词，修饰可数名词。

10．If you 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.

　keep up with意为"跟上，不落后于"，表示并肩前进，并驾齐驱。如：

　　John finds it difficult to keep up with the rest of the class in maths.

　　Can you walk a little slower? I can't keep up with you.

　catch up with 是指在已经落后的情况下"追上，赶上"。如：

　　He was behind in his studies because of illness, but he is catching up with the others now.

11．Calcium, which is found in eggs, milk and other dairy products, is good for our bones and teeth.

①be good for意为"对......有好处"（反义短语为be bad for）如：