单选题Tom concluded his lecture

问题补充：

单选题Tomconcludedhislecture________thathecouldn’temphasizeenoughhowimportantoureffortswere.A.to sayB.sayingC.saidD.having said

答案：

B解析考查非谓语动词。根据句子结构可知可知此处saying做状语，say与逻辑主语之间是主动关系，故选择saying。