给下面的字选择正确的解释。

朽  A .腐烂    B.衰老    C.磨灭

永垂不朽____   老朽____   朽木____

阅读理解

    Look, there are some special days in April. April Fool's Day is on April 1^st. Children will have fun on that day. Easter is also in April. There will be an Easter party. Children will play many games. They will roll (滚动)Easter eggs and meet the Easter Bunny. What a happy party! When is the sports meet? It's on 21^st . That will be fun too. Everyone loves April.

由于血缘关系的亲疏不同，西周贵族集团形成的宗法等级序列应该是