#### Answer

a. Given any negative real number $s$, the cube root of $s$ is negative.
b. For any real number $s$, if $s$ is negative, then the cube root of $s$ is negative.
c. If a real number $s$ is negative, then the cube root of $s$ is negative.

#### Work Step by Step

Recall that a reference to $s$ (or to any variable) in the first half of a statement must be balanced by a reference to $s$ in the second half. Otherwise, the first mention of $s$ will be confusing and unnecessary.