7．In most towns today，you can see teenagers standing over electronic machines with flashing lights，shooting at spaceships from other planets and dropping bombs on strange monsters（恶魔）．The machines have names like Space Warrior，Dark Invader and so on．It used to be believed that damage was done only to those strange visitors from outer space，but now it seems that they are striking back．
Many teenagers like electronic games so much that they can't stop playing．They spend hours tightly holding the joystick controls and constantly pressing buttons marked"fire"．They develop pains on their fingers because of the constant pressure．They play and play that the pains have no chance to cure properly．The rapid wrist movement required to guide the spaceship across the screen causes another problem：The muscles of the wrist and arm become so inflamed and swollen（充血红肿） that they press against the bones．This condition is what doctors now call"Space Warrior's Wrist"．
Other strange aches and pains also are likely to affect the elbows and shoulders．
Another even more alarming problem is shown by the case of a 17-year-old girl which was recently reported in the British Medical Journal．She had been playing various kinds of electronic games for more than two hours a day．Her father repaired games and machines and she could use the cassettes and systems in his workshop as often as she liked．One day，after playing a game called Dark Invader，she lost consciousness（晕倒） and fell to the floor．
Doctors who examined her found she was suffering from an unusual illness caused by lights flashing at a particular frequency．
28．Electronic games are found very popular withD．
A．people living in towns
B．students studying in high schools
C．girls working in their father's workshops
D．young people
29．"Space Warrior's Wrist"is caused byA．
A．constantly pressing the buttons
B．rapidly moving across the screen
C．tightly holding the joystick controls
D．inflamed and swollen muscles of the wrist
30．The case of a 17-year-old girl given by the writer shows that the writerC．
A．supports playing electronic games
B．feels very sorry for the girl
C．disagreed with young people's playing electronic games
D．feels worried about young people's poor health
31．From the passage we can conclude that playing electronic games isB．
A．enjoyable and helpful to the study
B．exciting but harmful to the health and study
C．interesting but harmless to the eyes
D．amusing and satisfying．
