What is the relationship between Objective-C and C?

A. Objective-C is a replacement for C, rendering C obsolete
B. Objective-C and C are two distinct programming languages with no compatibility
C. Objective-C is a subset of C, allowing only a limited set of C features
D. Objective-C is a superset of C, allowing all C code to be compiled and used within Objective-C classes
Answer: 