参考答案如下：regarded，as，an。完整的句子为：The terrorists regarded the hostages as an ace in the hole.
正确完成这道题，有两个要点。第一是掌握“把......当做”“把......视为”“把......看做”的短语。该题是使用regard...as这个短语。表述这个意思的短语还有很多，下面我们就来看看。
1. look upon/on sth/sb as sth/sb It means "to consider something (or somebody) to be something (or somebody)". For example: She's looked upon as the leading authority on the subject. 她被视为这门学科的权威人士。
有的朋友在习题中用到了look on with这个短语，这个短语是“以...看待”的意思，不是“把...看作”的意思。It means "to consider sb/sth in a particular way. For example: They looked on his behaviour with contempt. 他们对他的行为不屑一顾。
2. view sb/sth as sb/sth It means "to think about sb/sth to be sb/sth". For example: When the car was first built, the design was viewed as highly original. 这辆车刚出时，其设计被看作是独具匠心。 同样也有朋友用到view...with这个短语。这个短语同look upon...with一样是(以某种方式)“看待”的意思。For example: She views him with suspicion. 她以怀疑的目光看待他。
3. take sb/sth as sb/sthIt means "to have a opinion of somthing". For example: She took what he's said as a compliment. 她把他所说的当做是荣誉。
很多朋友们用到了take...for这个短语。Take ...for这个短语是有把...看作的意思，但是它侧重于指“把...错误地认为”，“把...错误地看作”。It means "consider somebody or something to be somebody or something when you are wrong". 意思是误认为。Look at the following sentences: Even the experts took the painting for a genuine Van Gogh. 甚至是专家都把这画看做是Van Gogh的真迹。I took the woman with you for your sister. 我误认为和你在一起的那个人时你姐姐。Of course I didn't do it! What do you take me for? 那件事当然不是我干的。你把我当成什么人呀?
作为consider这个意思讲时，有一个短语我们可以积累。它是taken overall，意思是总的看来。例如：Taken overall, our performance is a success. 总的看来，我们的演出是成功的。
4. consider sb/sth (as) sb/sthIt means "to have a opinion of something". For example: This reward is considered as a great honour. 这项奖被视为极大的荣誉。He considers himself an expert on this subject. 他把自己看做是这门学科的专家。如果细心的朋友会发现第二个例句少了as这个单词，是个病句。不是的，consider sb/sth as sb/sth这个动词短语结构中的as时可以省略的。那么consider...as与consider... to be等同。例如刚才的第一个例句“This reward is considered as a great honour.”可以说为"This reward is considered to be a great honour." 同样句中的to be可以省略。
第二，就是注意不定冠词在名词前如果这个名词的音标的第一个音标是元音的话，就要用an，不要用a。
