练习题：
1.He proved himself a _____ successor to the former Prime Minister.
A.worthwhile B.worthiness C.worthy D.worth
2. You should have put the milk into the icebox, I expect it ______ undrinkable.
A. became B. had become
C. has become D. becomes
参考答案：
1.C
worthwhile意思是“值得花费时间、金钱或精力的。”worthy可以表示“值得尊重或考虑的”，用这一意思时通常做定语。worthiness是worthy的名词形式。worth用作表语，意思是“有某种价值的;值得(做某事)”。本句需要填入一个作定语的形容词，所以，C是正确答案。
2.C
你本该把牛奶放到冰里。我想现在这牛奶不能喝了。从句意分析，牛奶已经变质，不能喝了，属过去发生的动作对现在造成影响，再加上by now是现在完成时的典型时间状语，故选C)