“Mendacious” means not telling the truth; lying.
Option A is the correct answer because “false” means something that is not according with truth or fact, hence it is the correct answer.
Option B is incorrect because “fabricated” means to invent something in order to deceive, which is not the correct meaning of the word mendacious.
Option C is incorrect because “imaginary’ means something that is existing only in imagination, which is not relevant here.
Option D is incorrect because “horrible” means something that causes horror. Or is terrifying or shocking, which is incorrect for the given word.