单选题 He worked ______ at his task for weeks before he felt satisfied that the results would justify his long effort.
【正确答案】 D
【答案解析】(assiduously坚持不懈地，刻苦地)。句意为：他连续好几个星期坚持不懈地执行任务才觉得满意，因为结果表明他长时间的努力是值得的。A．occasionally偶尔；B． regularly定期地；C．patiently耐心地。