Everybody suffers (19)_______ the common cold. It is caused by viruses (20)_______ infect the nose, throat and sinuses. It's most common during the cold winter months and affects children and adults of all ages. (21)_______ people catch a cold two to four times a year. A cold (22)_______ starts with feeling tired, sneezing, coughing, and having a runny nose. You may not have a fever, or you may run a low fever. There is no cure for the common cold. Antibiotics don't work against viruses. All you can do to feel better is to treat your (23)_______. Colds usually last about one week (24)_______ can continue for as long as two weeks. They usually go away on their own. 
mn giúp mình với 

Cho biết x và y là hai đại lượng tỉ lệ thuận, khi x = 2 thì y = 6. Hệ số tỉ lệ k của y đối với x là:

giúp với:(

D

c