twenties 表示20几岁的时候或20几个
正在作准备, getting ready
in 年，月，季节， 早上， 下午， 傍晚
in 2008， in spring, in the morning/afternoon/evening
on 天（星期几， 日期）
on Monday/ January 6th
at 晚上， 几点钟
at night, at six o'clock
I was born in Beijing on March 19th, 1995.
1 twenty是20，数词
4 when and where were you born?
I was born on ...
另外两个不是很会，对不起
3.on是具体时间，on Tuesday morning
at一般用在钟点上，at 8 o'clock
in 表示一段时间 in a few years
希望你满意
地四个问题有语法错误
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