Because of erratic rainfall patterns and low water-holding capacities of soils in Florida, supplemental irrigation is required for producing most crops. A research team has developed five alternative water-management strategies for irrigating cropland in central Florida. A random sample of 100 agricultural engineers was interviewed and asked which of the strategies he or she believes would yield maximum productivity. A summary of their responses is shown in the table.

a. Find a 90% confidence interval for the true proportion of agricultural engineers who recommend strategy C.

b. Find a 90% confidence interval for the difference between the true proportions of agricultural engineers who recommend strategies E and B.

c. Find a 90% confidence interval for the true difference between the percentages of agricultural engineers who recommend strategies A and D.