Have you decided ——————for Canada?A,when you will leave B.when you leaving选A是的,那能不能选B?

Have you decided ——————for Canada?A,when you will leave B.when you leaving选A是的,那能不能选B?
Have you decided ——————for Canada?A,when you will leave B.when you leaving
选A是的,那能不能选B?

Have you decided ——————for Canada?A,when you will leave B.when you leaving选A是的,那能不能选B?
decide后面接的是一个宾语从句,既然是一个句子,就必须有谓语,如果选B的话,谓语就没理由,如果是When you are leaving 的话,就对了

如果选B，从句缺少谓语动词be , When you are leaving 或 When you leave

have you decided 后跟when 引导的宾语从句， 从句要有谓语， will leave 作谓语。 而 leaving 不能作谓语 ， 如果改成 you are leaving 就正确了。
所以正确答案为A。

Have you decided when you will leave for Canada？
答案选A，宾语从句后面必须是一句完整的句子，而B选项不是一句完整的句子