What is the central claim of the passage?

Trade pays off based on what each side gives up, not on who is better. (The last two lines state it: the idea "does not reward being best. It rewards giving up the least.")

According to the passage, the doctor is

better than the gardener at both medicine and weeding (The first paragraph says she is better at medicine "and, as it happens, she is also faster at weeding a flower bed.")

What does the passage imply about a country that produces everything less efficiently than its trading partner?

It can still gain from trade, because it gives up less by specializing. (The gardener is worse at everything and still gains, because his sacrifice is smaller. The passage says the same logic scales up to countries.)

As used here, "sacrifice" means

what a person gives up by choosing one task over another (The paragraph defines it by example: an hour weeding is an hour not treating patients. The sacrifice is the forgone task.)

Two Tasks, One Worker: Level 4 Reading Comprehension Questions

Imagine two neighbors, a doctor and a gardener. The doctor is better than the gardener at medicine, and, as it happens, she is also faster at weeding a flower bed. Since she is better at both tasks, common sense says she should simply do both. Economics says otherwise.

What matters is not who is better in absolute terms, but what each person gives up. An hour the doctor spends weeding is an hour not spent treating patients, and that hour of medicine is worth far more than the weeding. For the gardener, an hour of weeding costs him almost nothing else, because he has no medical practice to abandon. His disadvantage in every task is real, yet his sacrifice is smaller. That relative cheapness is called comparative advantage.

So both neighbors gain when the doctor treats patients, the gardener weeds, and the two of them trade. The same logic scales up to countries. A wealthy nation can be more productive than a poorer one at building aircraft and at sewing shirts, and still end up richer by building aircraft and buying shirts.

The idea is hard to accept precisely because it does not reward being best. It rewards giving up the least.

Comprehension questions