选择A。该句的意思是大部分被邀请参加贝蒂生日宴会的客人是她的同学。注意：这里用到了定语从句，而定语从句又是对Most of the guests在起限定作用。邀请的主语是Betty,宾语是guests，guests是是被邀请的，所以原句可以这么理解，Most of the guests ___(who were )invited___ to Betty's birthday party were her classmates. 定语从句的主语谓语可以省略，所以省略了就是原文的Most of the guests ___ invited___ to Betty's birthday party were her classmates.ha...
