Ответ:
Task 1.
A - 5; B - 7; C- 2; D - 6; E - 8; F - 14; G - 4; H - 15; I - 12; J - 1; K - 3; L - 13; M - 11; N - 10; O - 9.
Task 2.
1) how
2) may
3) themselves
4) for
5) instead of
6) however
7) can
8) worse
9) addicted
10) which
11) impact
Task 3.
1) You mustn't stay in front of the computer for longs hours. It damages your eyes.
2) If you chat more than 8 hours a day, you will be addicted. It affects your school results.
3) You can use your internet as a source of information or to communicate with friends. However, you should sit without any physical activity.
4) You should be in contact with real world.