问题之一：I sit down, sign up for all my classes, get into them, and I'm happy.

我的疑问：sign 是不及物动词为什么不直接用 sign for, 而一定要加上副词 up 呢？

解答：sign up 是固定搭配（短语动词），意思是“报名参加”，若表示报名参加……，其后通常接介词 for 或不定式。如：

I’ve signed up for a pottery course. 我已经报名上陶艺班。

Shall I sign you up for the workshop too? 我要不要也替你报名参加讲习班？

I’m thinking of signing up for a yoga course. 我在考虑报名参加一门瑜伽课。

I’ve signed up to take a course at the local college. 我已报名在当地学院学一门课程。

Over half the people who signed up to do engineering were women. 报名读工程学的人半数以上为女性。

比较：没有 up 的 sign for，意思是“签收”。如：

You have to sign for it in person. 你必须亲自签收。

The postman asked me to sign for the parcel. 邮递员让我签字领包裹。

A registered letter must be signed for by recipient. 挂号信须由收件人签收。

This is a registered letter—someone will have to sign for it. 这是封挂号信，必须有人签收。

问题之二：And it remains to be seen whether large numbers of younger, healthier Americans will sign up for coverage.

我的疑问：这里的 for coverage 又怎么解释呢？又怎么翻译做什么成分？

回答：sign up for 的用法上面已提到过了，这里的 coverage 意思是“课程内容”（the range of subjects and facts included in a book, programme, class etc）。所以 sign up for coverage 的可以翻译成“报名参加听课”或“报名听课”。至于句子成分，可以将 coverage 分析为 sign up for 的宾语。