Why can’t you catch my question —Sorry I _______a magazine

It is required that you____ change the plan. —Oh, no! Why____ I follow you again?

Edison was a clever boy, and ______ he was fourteen, he had learned advance mathematics by himself

许多同学都有自己的电子邮箱，如168@sina.com, pgbook@ 163.com, hifriend998 @ 126.com 等。请问其中的@表示什么意思，该怎么读

He was so when he heard the ______news that he got the first prize in the contest.