This is a problem of chickens and rabbits in the same cage.

Let's talk about the first category: one is an animal with two feet-chickens and ducks.

The other is an animal with four feet-cows and sheep.

Second, you can use the hypothesis method.

Suppose this group of animals are all chickens and ducks, and * * * has 2× 1000=2000 feet.

The difference from the actual number of feet is: 2600-2000=600.

So there are cattle and sheep 600÷(4-2)=300.

Then 1000-300=700 chickens and ducks.

A: There are 700 chickens and ducks and 0/00 cattle and sheep.