Of the three listed, monotremes have the least derived way of bearing offspring, producing eatery eggs like those of many reptiles. Marsupials have a more derived form of reproduction, with their young gestating for a short time in the mother’s uterus and then in a protected body pouch. Eutherians has the most derived form with a long period of gestation and the new animal nourished via a large and intricate placenta.
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This question is asking for a summary of the information on different kinds of mammals as described on pp. 736-737.