Which hypothesis is least likely to explain the rapid evolution of morphological diversity during the cambrian explosion? select one: a. regulatory genes underwent major evolutionary change. b. morphological changes led to novel interactions among species. c. a mass extinction opened up ecological niche space, allowing an evolutionary radiation of animals. d. predation selected for enhanced diversity of defensive phenotypes. e. environmental oxygen increased.

answer: accepted answer: aquatic animals use the oxygen dissolved in water to carry out respiration. since the amount of dissolved oxygen in water is low as compared to the amount of oxygen in the air, therefore the rate of breathing in aquatic animals is much faster than it is in terrestrial animals.

explanation:

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

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