Key Concept: Cropping systems differ mainly in whether crops share the field at the SAME time or in sequence.
Why it's correct: Intercropping means growing two or more crops together, simultaneously, in the same field — e.g. maize with beans, boosting resource use and yield.
Why others fail: Monocropping uses only one crop; sequential and relay cropping both grow crops one after another over time, not truly at the same time in the same space.