Which of the following statements is​ correct? A. GDP includes nonmarket production but is not a measure of a​ nation's overall welfare. B. GDP includes nonmarket production and is therefore a good measure of a​ nation's overall welfare. C. GDP excludes nonmarket production but is usually considered a good measure of a​ nation's overall welfare. D. GDP excludes nonmarket production and is not a measure of a​ nation's overall welfare.