Explanation:

- A budget line illustrates the different combinations of two goods a consumer can afford with a given income and prices.

- Option 1: Price ratio - The budget line’s slope represents the price ratio of the two goods. This shows how much of one good you must give up to obtain more of the other.

- Option 2: Income ratio - Not typically used to describe the budget line. The line assumes fixed income altering expenditure choices.

- Option 3: Cost ratio - Like price ratio, but focusing on production and input costs, not consumer choices.

- Option 4: None of these - The budget line is linked to consumer’s choices, so options likely explain aspects.