Today, the average age of menarche in the United States is 12.6 among white girls, 12.1 for black girls and 12.2 for Mexican-American girls.是什么意思_Today, the average age of menarche in the United States is 12.6 among white girls, 12.1 for black girls and 12.2 for Mexican-American girls.在线翻译_英语_读音_用法_例句