Answer: C
Explanation:
The difference between an equation and expression is the equals sign. A simple way to tell of an expression is an equation is if there is an equal sign. If there is an equal sign, then it is an equation. If not, it is an expression.
Since this problem is asking for expression, it would be easiest to find an answer choice that doesn't include the word "_____is _____". This is a way to say _____ is equal to ____.
Let's go through each of the answer choices and write the equation/expression for it.
A. Equation
(4+x)/2=12
---------------------------------------------------------------------------------------------------------
B. Equation
p-1=14
---------------------------------------------------------------------------------------------------------
C. Expression
3c-9
---------------------------------------------------------------------------------------------------------
D. Equation
9m=36
---------------------------------------------------------------------------------------------------------
There is no indication that the expression is equal to anything, therefore C is the correct answer.