Treat this paragraph as a chain of causes, each link handing something to the next. The opener i states the topic, food and population. The closer vi says "they fall an easy prey to all sorts of diseases", and that "they" must belong to someone named just before it. Working backwards from that pronoun, plus the rule that a principle is stated before it is applied, orders all four middle sentences.
Read together: "The problem of food is intimately connected with population; the market is governed by demand and supply; if too many people demand goods to go round, prices will rise and poor classes will starve; wages will seldom rise in proportion to the rising prices; without enough food, such people lack health, strength of efficiency; they fall an easy prey to all sorts of diseases."
Let's summarize:
The middle sentences therefore run iii, v, ii, iv, and option (A) is correct.