could
1、这句的主语是I,谓语是could hear,宾语从句是what he said.反义疑问针对的是could
2、当陈述部分有never,seldom,hardly,few,little,barely,scarcely,nothing 等否定意义的词时,后面的反意疑问句则为肯定形式.此题中式hardly,故,反义疑问部分用肯定.
故而,答案为could