For each of the following hypotheses, explain whether it is a null hypothesis or an alternative hypothesis:
a. For females, the population mean on the political ideology scale is equal to 4.0.
b. For males, the population proportion who support the death penalty is larger than 0.50.
c. The diet has an effect, the population mean change in weight being less than 0.
d. For all Subway (submarine sandwich) stores worldwide, the difference between sales this month and in the corresponding month a year ago has a mean of 0.