Do you know the saying “No pain no gain（不辛苦，无收获）”？ What does it mean？ If you want to succeed（成功） in something， you must work hard. Animals also know this saying. Some of them are busy taking care of babies. Some work hard to build a house. Some travel a long way to find a warm place for winter. Who are they？

Ants are small， but they usually have a big family. Different ants have different jobs.

The worker ants（公蚁） are the most hardworking members. They have to build houses， look for food and take care of baby ants. They have strong mouths. They can use them to carry food 10 to 50 times heavier than their own weight（重量）.

It is not an easy job for parents to take care of their kids. But most rabbits do this job their whole lifetime（一生）.

Female（雌性的） rabbit gives birth to four to six babies each time. And she litters（產仔） about seven times a year. Rabbit parents have so many babies. They almost spend their whole life taking care of them.

Meet the animal master（大师） builders（建筑师）， the beavers（河狸）！ Most beavers live in North America. They like to build houses on rivers in late autumn. They cut down trees with their strong teeth and make them fall on the river. Then， they can build houses with mud（泥土）， branches（树枝） and leaves. When the river freezes（结冰）， their house is complete.