Answer the following question given this paragraph: 

There are about 50,000 vertebrate species, and they are placed in nine different classes. Five of the classes are fish. The other classes are amphibians, reptiles, birds, and mammals. Table below lists some of the distinguishing traits of each class.


Q: There are about 50,000 vertebrate species, and they are placed in how many different classes?

 Choices:

- four

- ten

- three

- nine

A:
nine
