For years , many people would not believe that smoke could attack so many parts of the body in so many ways . Study shows , however , that tobacco isn’t one single thing .  At least 60% of it is gas—20 different kinds of gas . And one of these is the deadly carbon monoxide (CO) （一氧化碳）.
In factories , the amount of this gas in the air is measured , and it must be kept under fixed , safe level . But there is 640 times this safe amount in cigarette smoke .
Oxygen is carried through your body by the red blood cells . But this poison gas , CO, will get to the blood cells before the oxygen can . So , if you smoke your blood carries five to ten times more of this deadly gas than is normal . To make up for this , your body must make more red cells .
The oxygen in your blood passes into your tissues（组织）. But here again CO makes trouble . It keeps the oxygen from passing into your tissues as fast as it should . Because of this , cigarette country is always about 8000 feet above sea level . Someone who smokes and lives at sea level gets as little oxygen as a nonsmoker at an altitude（高度）of nearly two miles .This happens to everyone who smokes , no matter how old or how young . Anyone who competes in sports can tell you that those who smoke run out of breath more quickly than those who do not .
1．The gas amount in cigarette smoke is______________.
A．640 times higher than the gas safe levels in factories
B．640 times lower than the gas safe levels in factories
C．640 times as much as that in factories
D．as dangerous as that in factories
2．If you smoke , ______________ .
A．your blood carries more oxygen than is normal
B．your blood carries much more CO than is normal
C．you can have five to ten times of blood than usual
D．your blood will be poisonous
3．Those who smoke______________.
A．all live at sea level
B．don’t live at an altitude of two miles
C．breathe as much oxygen as non-smokers
D．only get the same amount of oxygen at the sea level as non-smokers at an altitude of nearly 2 miles
4．Smokers are______________.
A．easily hurt              B．easily excited      C．easily tired         D．healthy