What is the best exercise to improve muscular strength and endurance?

Which of the following represents the results of a review of well-controlled studies of vitamin c supplementation on the resistance to, and recovery from, colds? there was a reduction in the duration of colds by 50% on the average. there was a slight effect on reducing the duration and severity of colds for people taking vitamin c supplements. there was a significant reduction in the duration of colds in people who consumed at least one gram a day. there was a significant reduction in the number of colds only in people who consumed > three grams per day.