下图是春秋空首布（一种货币），从这枚货币上我们能得到的有效信息有（    ）

①春秋时期已经掌握了冶铁技术  ②春秋时期金属货币已经得到广泛流通  ③春秋时期各诸侯国使用的是统一的货币  ④春秋时期商品交换比较活跃

如图是人体某处物质交换示意图，下列说法正确的是（　　）

精神文明建设的重要性。

Valentine's Day(情人节) is on February 14th every year. On this day, people send valentines(情人卡)to their loved ones, Valentine's Day is a special time to tell how much you care about a person.
Many people send candy in hearted shaped("心"状的)boxes to people they love. Flowers are also presents that people send on Valentine's Day. Valentine cards with words are often used by many people.
Can you guess who gets the greatest number of Valentine cards in the United States each year? Is it mother or father, sister or brother? Is it uncle or aunt? Is it the special friend? No, it isn't!
Mothers get a lot of cards, but school teachers get the most each year. Do you know who sends the most? Children do. Children send five times as many on February 14th as adults do.