Which one of the following statements is FALSE?
A. An unambiguous context-free grammar always has a unique parse tree for each string of the language generated by it.
B. There exist context-free languages such that all the context-free grammar generating them is ambiguous.
C. A finite set of strings from one alphabet is always a regular language.
D. Both deterministic and non-deterministic pushdown automata always accept the same set of languages.