答案：continuous
continuous和continual的区别：
(1)搭配区别：
continuous做表语和定语 be continious或continious+名词
continual只做定语 continual+名词
(2)词意的不同：
continual:反复,不停止(happen repeatedly)
eg:continual knocks on the door反复的敲门声
continous:连续性的=unbroken(lack of interruption)
eg:a continuous line一条不间断的线
continuous pain/headache持续的痛/头痛
而continuing的含义是继续,例如：continuing education持续教育/继续教育
还有continuing development (sustainable development)
没有反复的含义
祝更上一层楼!