Answer:
b. increases
Step-by-step explanation:
As the time period of a sine wave decreases, the frequency increases.
Frequency and time period follow an inverse relationship. Larger the time period, lower is the frequency and vice versa. Frequency measure the number of repetitions of the wave per unit time. Time period measures the time taken to complete one cycle of the sine wave. So larger the time to complete one cycle, smaller will be the number of cycles completed in unit time.