The leaf area index is the ratio of the A. upper leaf surface of a single plant divided by the surface area of the land on which the plant grows B. lower leaf surface of a single plant divided by the surface area of the land on which the plant grows C. upper leaf surface of a single plant multiplied by the surface area of the land on which the plant grows D. lower leaf surface of a single plant multiplied by the surface area of the land on which the plant grows