Answer the following question given this paragraph: 

Different types of bacteria stain a different color when Gram stain is applied to them. This makes them easy to identify. Some stain purple and some stain red, as you can see in Figure below . The two types differ in their outer layers. This explains why they stain differently.


Q: What is a gram stain used to identify ?

 Choices:

- radioactivity

- acids or bases

- different types of liquids

- different types of bacteria

A:
different types of bacteria
