Concept:Occupation refers to the regular economic activity a person performs to earn a living.
Explanation:The three main classes of occupation are industry, commerce, and service.
Industry involves the production, processing, and construction of goods.
Commerce covers trade, distribution, transport, and banking.
Services are professional and personal activities such as teaching and medicine.
Together, these three groups make the complete classification of occupations.
Answer:Industry, commerce and services (Option D).