Tina: What did you do yesterday?
Zack: You know how I've been sneezing so much. I went to the doctor to find out what I was allergic to.
Tina: How does the doctor know what you are allergic to?
Zack: The doctor did skin testing.
Tina: What's that?
Zack: I didn't know about skin testing before I went to the doctor. The doctor explained it to me before I had the test. Now I know all about it.
Tina: Tell me!
Zack: Well, the nurse had little bottles of things I might be allergic too, like trees, grasses, dogs and cats.