你要分清哪些是规则的、哪些是不规则的。像你现在列出来的不规则的有：
spend spent spent
sit sat sat
teach taught taught
forget forgot forgotten
sit sit sit
其他都是规则的，加-ed（但是要分情况，譬如有e直接加d，shared、provided；双写最后一个字母，dropped；变y为i再加ed，worried）
上述单词原形、现在分词、过去式、过去分词依次对应为：
climb climbing climbed climbed
share sharing shared shared
cook cooking cooked cooked
worry worrying worried worried
teach teaching teached teached
cause causing caused caused
break breaking broke broken
chat chatting chatted chatted
provide providing provided provied
sit sitting sit sit
leave leaving left left
forget forgetting forgot forgotten
spend spending spent spent
drop dropping dropped dropped
不规则动词过去式表可以参考：
http://blog.sina.com.cn/s/blog_3ec9fe690100cpk3.html~type=v5_one&label=rela_prevarticle