The "what to produce" problem in economics revolves around the decision of what goods and services should be produced in an economy. This decision is central to any economic system, as it determines which products should be prioritized and in what quantities, based on consumer demand and available resources.
The choice of "what to produce" depends on various factors, including market needs, resource allocation, and societal preferences. Producers must assess the types of goods to produce and the quantities required to meet the demand of consumers in the market.
Other questions such as "what technique to use" or "for whom to produce" address different aspects of production. These fall under the "how to produce" and "for whom to produce" categories, respectively, which focus on production methods and distribution to various groups in society.
Therefore, the correct answer is (B) for "how to produce" and (D) for "for whom to produce," as they deal with the practical aspects of implementing the production decisions made in response to the "what to produce" problem.