当that作learn,suggest,explain,agree,wonder,prove,mean,state,feel,hold等动词的宾语时;当宾语从句较长时;当主语状语置于主句尾,宾语从句之前时;当主语谓语动词(包括非谓语动词)与宾语从句之间有插入语时;当一个动...