1. begin的确有被动。2. 具体解释:1)begin既可以作不及物动词,如:the class begins和the movie begins等。2)但是它也可以做及物动词,用法类似于start,后面可以直接加宾语。如:I began my class with a humorous story.变成被动即为:My class was begun with a joke (by me).3)不过用做不及物动词时居多,上句的确也可以写成:My class began with a humorous story.3. 楼主所给的例题即是begin做及物动词。该句采用了状语从句的省略语法,即:Once begun nothing can be done to change it.=Once (it is begun) nothing can be done to change it.如果此题begin为不及物动词,则没法采用该语法,因为状语从句省略时,要求从句的谓语动词必须以be动词开头。参考资料:原创回答团(第159号会员)来自:求助得到的回答