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Not only tells you that the second part of the sentence will continue in the same direction as, and expand upon, the first part of the sentence. The first part says an exhibit showed a vegetarian diet is healthy, so the second part will also say the exhibit showed something positive about a vegetarian diet, and it will likely be relevant to health. Remorse and contrition are synonymous but are too negative. Mendacity, which means deception, and persecution, which means an attack on an ethnic group, are also too negative to be extensions of health benefits. On the other hand, vitality and vigor both mean having lots of energy, which is a congruous and logical extension of the health benefits of a diet.