弟弟用英文怎么说妹妹用英文怎么说

"弟弟"用英语表示为"younger brother"，来源是英语中"younger"和"brother"的结合。

例句：

My younger brother is in high school. (我的弟弟在上高中。)
He is three years younger than me. (他比我小三岁。)

"妹妹"用英语表示为"younger sister"，来源是英语中"younger"和"sister"的结合。

例句：

I have a younger sister who is very talented. (我有一个非常有才华的妹妹。)
My younger sister is a freshman in college. (我的妹妹是大学新生。)