Why is a high-quality bond typically considered a lower-risk investment than a stock?
a.) a bond typically pays a fixed, predictable amount of interest each year.
b.) stocks are stable and do not change often.
c.) bonds are issued by many different entities .
d.) well-established company stocks pay dividends to their investors.

The answer is A.
There is risk involved in owning a stock, and many unknown variables. The value of the stock could plummet, putting your principal investment at risk. There is no guarantee of return on investment, and even well-established companies have had to cut dividends during difficult times.

In the case of bonds, you are guaranteed by the bond issuer that your principal and the agreed-upon interest will be paid at a defined time. Excluding the event of bankruptcy (and still likely in this case), you are virtually guaranteed that the entity will pay you according to the agreed-upon terms. For this reason, bonds are considered a much lower risk investment.

Why then, do many people choose to invest at least part of their portfolio in stocks? Stocks generally have a much high expected return, and many people consider this increased return worth the increased risk that with it. 

The answer is a. i think