Please answer the following question: Read the following article and select the best answer. Article: You know eating fruit and vegetables is virtuous. But did you know it can also make you look good? People who increased their intake over just six weeks developed a healthy glow and appeared more attractive, researchers found. Scientists at St Andrews University found eating them subtly increased yellow and red pigments in the volunteers' skin. They monitored the food intake of 35 people and took pictures of their faces, arms and hands using a sensitive camera at the start, and after three and six weeks. Increasing their intake of greens by 2.9 portions a day was found to make the person look healthier and an extra 3.3 portion could enhance their attractiveness, when their photographs were rated by others. Fruit and vegetables are rich in carotenoids , which are known to protect against cell damage from pollution and UV rays, and can also prevent age-related diseases including heart disease and cancer. But while it was known eating extreme amounts of certain vegetables such as carrots could turn skin orange, it was not known a small increase was perceptible to others and was seen as _ . A camera measured changes to the skin's redness, yellowness and lightness, and found it significantly changed in people who naturally increased their intake. These changes were not evident at three weeks. Using light sensors, the researchers showed these red and yellow hues(,) were linked with the levels of carotenoids in their skin. There are hundreds of carotenoids but those thought to have the most dramatic effect are lycopene which gives tomatoes and red peppers their red color1 - and beta-carotene found in carrots as well as broccoli, squash, and spinach. Skin color1 is also affected by chemicals called polyphenols , found in apples, blueberries and cherries, which cause blood rush to the skin surface. Question: The red and yellow color1s were related to _ in their skin. - the contents of intake - the levels of carrots - the time of eating fruit and vegetables - the amount of carotenoids
A:
the amount of carotenoids