doubt n. 怀疑，疑惑，疑问 v．怀疑，不信，拿不准
例句：There is no doubt that we will be successful.
毫无疑问我们会成功的。

suspect n．嫌疑犯 喇，令人怀疑的，不可信的 v．怀疑，猜想，对……有所觉察
例句：Carry has more intelligence than we suspected her to possess.
凯丽的智慧比我们猜想的要高。

suspicion n. 猜疑，怀疑
例句：Police intercepted the traffic on the roads to examine vehicles under suspicion.
警察在路上拦截过往车辆，以搜查可疑的车。

suspicious adj. 可疑的，怀疑的
例句：The police found no suspicious document whatsoever.
警察未发现任何可怀疑的文件。

dubious adj．可疑的，不确定的
例句：The results of this policy will remain dubious for a while.
这项政策的效果短期内难以确定。

doubtful adj. 可疑的，不确的，疑心的
例句：I am doubtful about the propriety of granting such a request.
我怀疑答应这项要求是否合适。

doubtless adj. 无疑的，确定的 adv. 无疑地，确定地
例句：The plaudits he received was doubtless worthy of his fame.
他所得到的喝彩肯定是同他的声誉相符的。

undoubtedly adv. 毋庸置疑地，的确地
例句：Carina's teachers told her to work harder, or She would undoubtedly fail her exam．
卡瑞娜的老师要她加把劲儿，不然考试准不及格。

skeptical adj. 怀疑性的，好怀疑的
例句：Many skeptical progressives refuse to agree that the foregoing reform sufficed.
许多持怀疑态度的进步分子认为，上述改革是不够的。