Answer:
Option C is correct
speed(memory) or s(m)
Explanation:
Dependent variable states that a variable whose value dependent upon the dependent variable.
For example:

x is the independent variable and f(x) is the dependent variable
Given the statement:
The speed of a computer depends on the amount of memory.
Let m represents the amount of memory and s represents the speed of a computer.
m = Independent variable
s(m) = Dependent variable on m
Then
the most appropriate name for the function described is:
speed(memory) or s(m)