Answer: B. Loss of earnings from employment
Explanation:
Opportunity cost refers to the loss of other alternatives when another alternative is being chosen. It is the potential benefit that an individual, firm or government misses out on when a different alternative is being selected.
Based on the question given, the opportunity costs for David when he started his business will be the earnings that he got from his previous employment such as the wages or the salaries, bonuses etc. Since he has began his own business, he can't enjoy those benefits anymore.