Some research suggests that individuals who take both vitamin C and zinc at the onset of the common cold experience fewer cold symptoms and recover more quickly than those who do not take these nutrients. What is the best explanation for why vitamin C and zinc could reduce the intensity and duration of the common cold?

A. Both vitamin C and zinc are involved in wound recovery.
B. Vitamin C and zinc are required for the absorption of vitamin K, which is needed for wound recovery.
C. Vitamin C and zinc are required for the absorption of iron, which is needed by the immune system.
D. Both vitamin C and zinc are involved in immune system functions.