Classify the experiments according to their experimental designs. Some designs may be used more than once. Vitamins: A sample of 50 children was separated into boys and girls. The members of each group were randomly assigned to two different vitamin supplements. The responses of each child were recorded at the completion of the experiment. Rats: A sample of 50 rats was grouped into pairs of similar individuals based on species, age, and weight. Then, within these pairs, each rat was assigned to a different diet. After three weeks, the responses of each pair were analyzed to compare the effects of the diets. Track spikes: Twenty runners were assigned to run two laps, once with track spikes and once without track spikes. The order of treatments was randomized for each runner. The lap times of each runner were recorded to compare the effects of the two different treatments. Street segments: A random sample of 100 street segments was selected in each of two cities. To compare the street tree populations of the two cities, the diameter and species of all trees in each street segment were recorded. Documentaries: Eighteen volunteers were randomly assigned to three groups, and each group watched a different documentary about feminism. After completing the documentary, each volunteer was asked if their views on feminism were influenced by the film.