ANSWER : B
I cannot find better explanation than the one provided by @algo.coder;
1-The question state that one statement is true : "which" can be plural but the "is" tells you that only one is true -> So c is excluded
2- a is stating that only ONE statement is false, but you got three statements and the question tells you that only one is true so 2 are false -> So a is excluded
3- b is correct : it says that two statements are false (a and c) and it is in accordance with the question (only one can be true).
Stay tuned for another ''Brain Game''