Mr．Smith has a lot of business _________．I know by _________ that this man cannot be trusted．
A.experience; experienceB.experiences; experienceC.experience; experiencesD.experiences; experiences在线课程A
解析：
本题考查名词的用法。名词experience表示“经验”时，为不可数名词；
表示“经历”时，是可数名词。