Which line of code should you use?

You have a class named Customer and a variable named customers.
You need to test whether the customers’ variable is a generic list of Customer objects.
Which line of code should you use?

A.
Option A

B.
Option B

C.
Option C

D.
Option D

Explanation:
http://stackoverflow.com/questions/982487/testing-if-object-is-of-generic-type-in-c-sharp