use the concepts of gross and net investment to distinguish between an economy that has a rising stock of capital and one that has a falling stock of capital. Explain: "Though net investment can be positive, negative, or zero, it is impossible for gross investment to be less than zero."

Gross investment can be zero but never negative because it is the investment in the capital stock.

Explanation:

Gross investment in a country is the amount that has been spent by the economy on the fixed assets of the economy in a given period of time. It is the addition done to the total capital stock of the country in a particular period of time.

So this shows that it can be zero meaning that no amount is spent on the addition of the capital stock in a particular period of time but it can never be negative.