第二十一英文怎么说读

"第二十一"在英语中读作 "twenty-one"。
来源是由二十和一两个单词组合而成。
例句:

He is 21 years old. 他21岁了。
The 21st century has been marked by rapid technological advancements. 21世纪以快速的技术进步而闻名。
The 21st of June is the summer solstice. 6月21日是夏至。