The happiest thing during the Spring Festival
过年最开心的一件事
This is the happiest thing for me during the Spring Festival
这就是我过年最开心的一件事
I think it will be unforgettable for me
我想它会使我难忘
be unforgettable for sb.
使某人难忘make sb forget 是不是使某人难忘的意思？没啊，相反，它是使人忘记的意思哦哦！！