单选题 On hearing of the case some time later, Conan Doyle was convinced that the man was not guilty, and immediately went to work to ascertain the truth.
【正确答案】 C
【答案解析】[解析] 各项的意思是：explore“探测，探究”；obtain“获得，得到”；verify“检验，查证”；search“搜索，调查”。划线单词ascertain的意思是：确定，探知。句意是：听到这个案子一段时间之后，Conan Doyle确信这个男人是无罪的，便立即着手调查真相。所以，答案是C。