20 points a population of mussels was observed in a particular ecosystem. it was found that crabs preferred these mussels as their favorite food. few mussels developed a thicker shell to protect themselves from crabs found in the region. which three statements does this adaptation suggest? a. a change in the environment led to a new distribution of traits in a population. b. the trait of shell thickening underwent natural selection. c. the trait for shell thickening will not be selected by future mussel generations. d. half of the mussel population developed the trait while the other half did not. e. mussels with the shell thickening trait had a greater chance of survival.

Juan and carol were studying invertebrates in biology. they knew that segmented or earth worms preferred a dark, moist habitat. during this lab, they would be investigating the responses of organisms called planaria or dugesia tigrina. these were simple flatworms that still had a one-way digestive system and a very simple nervous system. juan and carol placed the planaria in a petri dish containing cool, distilled water that was partially covered with black paper. they shined a light on the dish. next, they removed the paper and placed a small amount of chicken liver at one end of the dish. they added a few large salt crystals to the water. finally, they added drops of hot water to the cool water in the petri dish. their results can be seen in the data table. according to their experiment, all but one conclusion is valid.