`1.` Because every year, about fifty million people have to go to the doctor because of headache

`=>` Căn cứ: Đoạn 1 `->` đoạn 2

`2.` They can see black dots or bright spots in front of their eyes

`=>` Căn cứ: Đoạn 4

`3.` Yes, they can

`=>` Căn cứ: Đoạn 5

`4.` They have headache when they work too hard or they are too nervous about something

`=>` Căn cứ: Đoạn 7

`5.` They can prevent headaches by changing their diets or their lifestyle or simply by going to bed

`=>` Căn cứ: Đoạn cuối

1. Because every year, about fifty million people have to go to the doctor because of headache.

    (Dựa vào thông tin ở câu số 2)

2. They can see black dots or bright spots in front of their eyes.

    (Dựa vào thông tin ở câu số 4)

3. Yes, they can

    (Dựa vào thông tin ở câu số 5)

4. They have headache when they work too hard or they are too nervous about something.

    (Dựa vào thông tin ở câu số 7)

5. They can prevent headaches by changing their diets or their lifestyle or simply by going to bed.

    (Dựa vào thông tin ở câu cuối)