begin的过去式是began,过去分词是begun。began为过去式,用于一般过去时,可独立作谓语,描述过去发生的动作,常搭配过去时间状语,如“She began to read the novel at 8 p.m.”。begun是过去分词,不能独立作谓语,需与助动词搭配:与have/has/had构成完成时态,强调动作从过去持续到现在或对现在的影响,如“They have begun to prepare for the exam”;也可与be动词构成被动语态,如“The construction...