=>
15. Yes, there is. 
-> There is only one disease called common : the common cold.
16. Because every year millions of people catch it. 
-> We call it the common cold because...it.
17. They are a runny nose, a slight fever, coughing and sneezing. 
-> Everybody knows the...sneezing.
18. We can eat well, exercise to prevent a cold. 
-> How can you help prevent a cold?...healthy.

15 Yes, there is. ( dẫn chứng câu số 1 đoạn 1)
16 Because every year millions of people catch it. ( dẫn chứng câu số 2 đoạn 1)
17 They are a runny nose, a slight fever, coughing and sneezing. ( dẫn chứng câu số 1 đoạn 2)
18 We can eat well, exercise to prevent a cold. ( dẫn chứng đoạn 3)