Answer:
I agree because investing in stocks provides the highest potential return for your investment. Even though the price of stocks might vary daily, sometimes it increases, other times it decreases, on the long run the price of stocks usually have an upward slope. This means that they tend to increase over time, and their value usually grows much more than any other type of investment.
Investing in stocks is usually a very good long term investment, since the price might decrease or stay still for relatively long periods of time (even a couple of years), but eventually they will rebound. So if you are patient enough and can wait for your investment to yield high returns, stocks are your best option.