Most living things need oxygento survive. these two body systems bring oxygen into your body and then move to all your body parts. what are these two body systems?

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.

During the past few weeks or months, have you noticed any exercises that have become too easy for you? do you think you need to increase the intensity in any of the three exercise areas in your workouts? evaluate your exercise progress in the three exercise areas (cardiovascular, resistance, and flexibility) and list what modifications, if any, you may need to make in your exercise routine.

(i think the answer is either b or d can someone me? i’ll mark you brainliest) signs tell you what you can or can't do, and what you must do. a. regulatory b. warning c. guide d. construction