C - Both is your answer.
Reason for A being the answer: Usually the more skillful the worker (in which they know and master a wider variety of skills), the more they are 'worth more' to the industry. In this case, the worker is generally paid more to be an incentive to stay at the place.
Reason for B being the answer: The more the Demand (such as having a large customer base), the larger the Supplied amount is needed. The more needed to produce, the more workers/shifts the industry needs. To draw more workers, the employer would either have to give higher wages or more work benefit.
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