would rather than为什么要用would啊? once opon a time,为什么要用once,帮我分析一下成分!

would应该是强调下，带有感情的成分在里面。
ONCE UPON A TIME，被当成一个固定词语，曾经，以前某个时候

这两个问题严格来讲是固定搭配,一般都是这么用的
在麦克米伦字典中查寻rather
4 BRITISH INFORMAL OLD-FASHIONED used for showing that you are eager to agree to what someone has suggested
rather than
used for saying that one thing is preferred to another or happens instead of another:
Doug chose to quit rather than admit that he'd made a mistake.
Rather than criticizing your husband,why not find out if there's something wrong?
We want the matter settled sooner rather than later.
would rather
used for saying that you would prefer to do something or you would prefer that something happened:
I'd rather you didn't mention this matter to anyone else.
He doesn't want to learn – he'd rather stay at home and play video games.
would rather...than:They said they would rather die than abandon their homes.
would rather not (=would prefer not to do something):You don't need to come if you'd rather not.
查询would 会发现would 可以用来给出可能的状况,可以表达批评某人的行为
once upon a time 是习语,需要记忆的
once upon a time
1 used for starting children's stories:
Once upon a time,in a faraway land,lived a beautiful princess.
2 SPOKEN used for talking about a situation that existed in the past but no longer exists,especially when it was better than the situation now:
Once upon a time,you could leave your doors unlocked at night and not worry about someone breaking in.