As crossing

While you cross

While crossing

Cross

这题考查时间状语从句的省略式，当主从句的主语一样时，可以省略从句的主语和be动词，这题的while crossing就省略了you are，句意是：当你过马路时，别忘了两边看看。选C。

It is well-known that crack cocaine is a powerful             drug and users become           to it much more easily if they smoke it.

addicted; addict

addictive; addict

addicted; addictive

addictive; addicted

考查形容词辨析。众所周知可卡因是一种强大的令人上瘾的毒品，如果使用者吸了它更容易上瘾得多。addicted上瘾的，着迷的；addict"shi使沉迷；使上瘾”是动词；addictive “使成瘾的，令人沉迷的”。第一空表示“令人上瘾的”用addictive，故排除A，C项；become addicted to “对....上瘾”，第二空填addicted。故选D项。

--- I'm afraid I can't complete the marathon next week.

---              ! You have been practicing a lot.

No problem

Go ahead

Cheer up

Good luck

考查交际用语。句意：---恐怕我下周不能完成马拉松比赛。---振作起来！你一直一直在不断练习。A.No problem没问题；B. Go  ahead请干吧；请便吧；C.Cheer up高兴起来；振作起来；D. Good luck祝您好运。由下文可知说话人担心，完不成马拉松比赛，由“你一直不断练习”可推断表示鼓励“振作起来”。故选C项。

Tom looks so pale today. He ______ ill.

must be

had to be

should be

shall be

[翻译]汤姆看起来脸色不好，他一定生病了。[解析] A 试题解析：情态动词must表示推测。题目中表示肯定的推测。

Small sailboats can easily turn over in the water ________.

if not managed carefully

if are not managed carefully

unless not managed carefully

unless are not managed carefully