One effect of the pesticide ddt upon birds is to inhibit the production of the enzyme carbonic anhydrase, which controls calcium metabolism. it is believed that this causes eggshells to be thinner and weaker than normal and makes the eggs more prone to breakage. an experiment was conducted where 16 sparrow hawks were fed a mixture of 3 ppm dieldrin and 15 ppm ddt (a combination often found in contaminated prey). the first egg laid by each bird was measured, and the mean shell thickness was found to be 0.19 mm. a "normal" eggshell has a mean thickness of 0.2 mm. the null and alternative hypotheses are