Answer:
(B) Increase the spring constant
Step-by-step explanation:
The frequency os oscillation of a block is given by the following formula:

In which k is the spring constant and m is the mass of the block.
So the answer is either b or c, as the frequency of oscillation is a function of the sping constant and of the mass of the block.
Lets try b first, increasing the spring constant.
For example, with m = 4.
If k = 16, w = 2.
If k = 36, w = 3
So as the sping constant increases, so does the frequency of oscillation.
So the correct answer is:
(B) Increase the spring constant
Why c is wrong?
Suppose we have k = 36.
if m = 4, w = 3
if m = 9, w = 2
So, as the mass increases, the frequency decreases. So c is wrong