列出算式，把相應的英语数字写在横线上。
　　There are two horses on the farm.
　　Two more horses come.
　　How many horses are there in all？
　　_______________________ horses
　　There are ten fish in the river.
　　Three fish swim away.
　　How many fish are left？
　　_______________________ fish
　　There are seven hens.
　　Eight more hens come.
　　How many hens are there in all？
　　_______________________ hens
　　There are eight dogs.
　　Four dogs go away.
　　How many dogs are left？
　　_______________________ dogs