Answer:
The correct answer is the option C: If Blake promotes Austin, it will leave another vacancy to fill.
Explanation:
To begin with, in the case that a vacancy is available in the company and that its manager needs to find a person for the job then the most probable thing to do is to look for someone through outside sources due to the fact that even though it might cost as well as promoting Austin, the fact of just promoting him will cause the fact of rising his wage and also looking for someone new to cover his old job and therefore to pay another one again. That is why, that instead of falling into two different actions it is better to just look for someone new.