I believe the correct answer is C. This piece of furniture is a chair. This chair is soft; all chairs are soft.
There is a fallacy of logos here, which means a mistake in logic. Just because that one particular chair is soft doesn't mean that all chairs are going to be soft just because they are all furniture. The softness of one chair cannot be applied to all chairs as furniture.
Although D could also be correct, the first part of the sentence is wrong, which makes the entire statement wrong, which is why you shouldn't pick it here.
