用it改写句子

it is difficult to give up smoking
it seems like they are attractive to some people when they are smoking.
it is believed that smoking cause cancer.
it is no use to quit a stressful day
it is astonishing that China produce one third of world cigarettes
it is illegal to advertise cigarettes in this country
it is wonderful that my dad quit smoking at last
it was dark and stormy when the old man started his journey
it's likely to suffer from bad health if you keep smoking.
it is necessary to take pills to control your blood pressure.