答：第二空肯定是released,第一个空if,once从语法、句意上讲都可以
if released =If he is released,...如果从监狱里放出来的话,他很有可能会重操旧业,再度犯罪.
Once released=Once he is released,.一旦从监狱里放出来,他很有可能会重操旧业,再度犯罪.
这是一个值得“推敲”的问题.用推,用敲,看上下文吧.
本人感觉用once要更好些.
搜索网络,本题为
高等教育自学考试英语语法试题
二、填空题 (本大题共 28小题,共36分 ) Section A:Fill in the blanks with the appropriate words given in the group.
之25题
25.if ,once,until,releases,releasing,released
______ ______ from prison,he is likely to engage himself in the same business and commit the same crime.
由四六级翻译和单词改编而来：
13.________________________ (一旦从监狱里放出来),he is likely to engage himself in the same business and commit the same crime.
所以,在出题者心中已经有答案了,就是：Once released