Nisha says farming and mining are "lower-grade" work, and a country only advances by moving…

Why

Nisha is picturing the three kinds of economic activity as a ladder — primary (farming, fishing, mining) at the bottom, then factories, then services at the top — and thinking progress means climbing away from the bottom. But they are not a ladder; they lean on each other. A country full of offices and IT firms still needs food grown, cotton picked, and iron and coal dug up — its factories cannot run and its workers cannot eat otherwise, so it either does that primary work itself or pays another country to. Test it: think of what a single day in a city depends on — the rice, vegetables, milk, cotton clothes, and metal in every bus and building all began as primary activity somewhere. Her brother is right: the primary sector is the foundation the others stand on, not a lower rung — the three depend on each other.