Alack of vitamin d is said to be detrimental to the maintenance of bone density. if a
scientist wanted to determine whether this view was supported by scientific evidence,
which of the following would be the best method of doing so?
(a) carry out a survey of people with normal bone density to find out whether they
take vitamin d tablets or not
(b) compare the bone density of two groups of people with low bone density after
providing only one of the groups with vitamin d
(c) compare the incidence of people with low bone density in two different populations
(d) carry out an experiment in which a group of people with normal bone density are
exposed to very little sunlight to prevent the production of vitamin d

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.