Answer
See explanation below.
Work Step by Step
(a) Consider $x$ and $y$ are two real numbers. For every real number $x$ there must exist a real number $y$ such that the product $x \cdot y=y$.
(b) When real number $x$ is non-negative and real number $y$ is negative then their difference $x-y$ will be positive.
(c) Consider $x$ and $y$ are two real numbers. For every real numbers $x$ and $y$ there must exist a real number $z$ such that sum of $y+z=x$.
