Which of the following is NOT the result of laboratory experiments

A． ozone levels and hospital admissions for asthmaB. hazy days and more asthma attacks in childrenC. the levels of particles in the air and death ratesD. high levels of pollution and more. symptoms

A．ozone and fall in lung function
B．ozone and lung diseases such as asthma
C．nitrogen dioxide and worse lung function
D．smog and chronic bronchitis and emphysema