Step 1: Alternate route: example-based contrast:
Take cotton as an example: growing cotton on a farm is a primary activity (direct extraction from land); weaving that cotton into cloth in a textile mill is a secondary activity (transformation into a new product).
Step 2: Generalise from the example:
Whenever an activity is the FIRST step of taking something from nature, it's primary; whenever an activity takes that natural output and physically changes/combines it into something new, it's secondary.
Step 3: Final Answer:
Primary = extraction stage (e.g. growing cotton); Secondary = transformation stage (e.g. weaving cotton into cloth) — the defining difference is whether the activity extracts from nature or processes what was already extracted.