For each of the following, write out the alternative hypothesis, being sure to indicate whether it is one-sided or two-sided.
a. Consumer Reports discovered that 20% of a certain computer model had warranty problems over the first three months. From a random sample, the manufacturer wants to know if a new model has improved that rate.
b. The last time a philanthropic agency requested donations, 4.75% of people responded. From a recent pilot mailing, they wonder if that rate has increased.
c. A student wants to know if other students on her campus prefer Coke or Pepsi.