The correct answers are B) to gain a comparative advantage and D) to increase efficiency.
The statements that best explain why producers choose to specialize are "to gain a comparative advantage and to increase efficiency."
If companies and producers specialize in specific products, they can better elaborate their goods, reduce costs and aim a specific target. This action has benefits for clients because they are going to find specific products in the market that benefit their needs at better prices. So when manufacturing the goods, these companies are going to increase their efficiency and will be able to gain a comparative advantage because they will be the only ones that produce the specific product, not their competitors.