Chu-lin's doctor tells her that her baby will have problems with its respiratory and digestive systems. the doctor explains that the problems originated when the zygote divided into the three major cell layers. evidently, in chu-lin's case, there was a problem in the formation of the

The answer is endoderm.

There is three type of germ layer in embryo, ectoderm(outside), mesoderm(middle), and endoderm(inside). The germ layer will dividing and maturing into different set of organs. The organ that derived from endoderm layer would be vary from gastrointestinal tract, respiratory tract, urinary tract, and auditory system.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."