Based on the above , the most reasonable conclusion is that Fluffy is a mammal.
Based on the above that the statement "If all cats are mammals and Fluffy is a cat," the most logical conclusion is a) Fluffy is a mammal. This is because the statement is one that tends to establishes a conditional relationship between cats and mammals, implying that every cat is also a mammal.
Hence, if we know that Fluffy is a cat, then we can figure out that Fluffy is also a kind of animal called a mammal. Fluffy is not a mammal. This goes against what the premise says. All mammals are not cats. This statement is different from the original and may not be true.