His job is_____as a detective
A.working B.to work
答案给的B，working 与to work 能换吗？这里怎么区别？

不定式作表语表示具体动作或将来动作；动名词作表语表示抽象的一般行为。
①To be kind to the enemy is to be cruel to the people.
②My chief purpose is to point out the difficulties ofthe matter.
③What I would suggest is to put off the meeting.
当主语和表语都是不定式时，其含义一是条件，一是结果（例①）。当主语是aim,duty,hope,idea,mista ke,plan,purpose,suggestion等为中心词的名词词组（例②）时，或以what引导的名词性分句（例③），不定 式说明主语的内容。
④Our work is serving the people.
⑤What he likes is taking a walk after supper.
⑥The story told by Mr.Wang is interesting.
④⑤句动名词作表语，与主语部分可以转换，如Serving thepeople is out work,而⑥句中是现在分词作 表语，说明主语的性质、状态，现在分词具有形容词的各种特征，另外，动名词作表语还应与进行时态区别开 来。