All of them are true, and here are some hints: (1) is any polynomial of degree at most 2 a pol. of degree at most 3? ; (b) Is every differentiable function a continuous one? ; (c) Is the set of all pol's of degree at most 2 with zero linear coefficient a vector space? ; (d) Is is true that any non-zero vector in any non-zero vector space is part of some basis?