State the null and alternative hypothesis for each conjecture:
a. A researcher thinks that if expectant mothers use vitamin pill, the birth weight of the babies will increase. The average birth weight if the population is 8.6 pounds.
b. An engineer hypothesis that the mean number of defects can be decreased in a manufacturing process of CDs by using robots instead of human for certain tasks. The mean number of defective disks per 1000 is 18.
c. A psychologist feels that playing sot music during a test will change the results of the test. The psychologist is not sure whether the grades will be higher or lower. In the past, the mean of the scores was 73.