Let's take a look at each option:
A.) Culture often changes very quickly. (Not true, culture takes many years to change.)
B.) Language is not a part of culture. (Language is a very important part of culture, as it defines the method of communication.)
C.) Culture does not include material things. (Culture can include material things, like tools, machines, art, and clothing.)
D.) Culture includes people's work, behavior, and beliefs. (Yes! Culture does include the work, behavior, and beliefs of the people.)
Therefore, the answer is D.
I hope I've helped! :)