Do not confuse suspicious, doubtful, and dubious. If you are suspicious of a person, you do not trust them and think they might be involved in something dishonest or illegal. I am suspicious of his intentions... Miss Lenaut had grown suspicious. If you describe something as suspicious, it suggests behaviour that is dishonest, illegal, or dangerous. He listened for any suspicious sounds. ...in suspicious circumstances. If you feel doubtful about something, you are unsure about it or about whether it will happen or be successful. Do you feel insecure and doubtful about your ability?... It was doubtful he would ever see her again. If you are dubious about something, you are not sure whether it is the right thing to do. Alison sounded very dubious... The men in charge were a bit dubious about taking women on. If you describe something as dubious, you think it is not completely honest, safe, or reliable. ...his dubious abilities as a teacher.

不要混淆 suspicious，doubtful 和 dubious。suspicious of sb 表示不信任某人，认为其可能和欺骗性行为或违法之事有牵连：I am suspicious of his intentions (我怀疑他的意图), Miss Lenaut had grown suspicious (莱诺小姐起了疑心)。suspicious 还可用来指某事具有欺骗性、违法或危险：He listened for any suspicious sounds (他仔细听有没有什么可疑的声音)，in suspicious circumstances (在可疑的情况下)。doubtful 表示不确定某事是否发生或是否成功：Do you feel insecure and doubtful about your ability? (你对自己的能力缺乏自信、感到怀疑吗)，It was doubtful he would ever see her again (不知他是否还能再见到她)。主语为人时，dubious 表示不确定是否该做某事：Alison sounded very dubious (艾利森听起来犹豫不决)，The men in charge were a bit dubious about taking women on (几位男主管有点拿不准要不要招女职工)。dubious 修饰事情时，表示该事不完全可信、安全或可靠：his dubious abilities as a teacher (他的教学能力令人怀疑)。