1. a sum will grow if loaned out at interest.
2. people prefer to have things now.
3. capital goods are productive in producing consumer goods.
4. goods to be received in the future are worth more than goods to be received now.
Choose the correct option.
The correct answer is 3. Capital goods produce output. So if we add to our stock of capital goods instead of consuming today, we could consume tomorrow not only those capital goods but the additional output produced by them. Since one always has the option of using funds not spent on consumption to add to one's own capital stock one would never loan these funds to someone else at zero interest.
Take a specific example. Suppose that instead of consuming 100 units of output we add 100 units to the stock of capital. If one unit of capital produces 0.1 units of output, we will have an additional 10 units of output next year as a result of having expanded the capital stock. This means that next year we could consume 110 units of output as a result of giving up 100 units of consumption this year. (This assumes, of course, that we choose to consume the 100 units of capital set aside this year in addition to the income it produces.) In view of this, it makes no sense to buy an asset that yields zero interest.
The statement that people want to have things now is at best ambiguous. People obviously want to have things in the future as well---otherwise, why would they be saving and adding to the economy's capital stock? Nevertheless, it could well be that people save only because interest rates are positive. If interest rates were zero people might well choose not to save and accumulate capital to augment future consumption. Interest rates are positive because by giving up consumption now people have the option of consuming at an increased rate tomorrow. No one would loan out funds at a zero rate of interest when those funds can be used to purchase capital goods that will yield increased income in the future.
Option 1 simply states that the interest rate is positive. It provides no statement as to why. If one is available, an option that deals with the question of why interest rates are positive is clearly a better choice.
Option 4 is wrong because goods to be received in the future are worth less than goods received now, not more. The fact that they are worth less is just another way of saying that the interest rate is positive.