Which of the following projects would be considered the least risky, assuming a hurdle rate of $12\%?$

a$."C\text{'}$s$"$ cost of capital exceeds its rate of return

b$."$A$"$ has a small, but negative, NPV

c$."$D$"$ has a zero NPV when discounted at $14\%$

d$."$B$"$ has a positive NPV when discounted at $10\%$