Correct answer choice is:
D. A frequency higher than the original frequency.
Explanation:
This is a true case of Doppler's effect. The Doppler effect can be defined as the effect originated by a traveling source of waves in which there is a visible higher variation in pulse for observers towards what the source is progressing and a visible descending shift in rate for observers from what the source is dropping.
It contains protease which is the enzyme that breaks down protein