单项选择题
A．the effect of smoking among children B．the difficulty in preventing children from smoking C．the reasons why children start smoking among children D．the measures to ban smoking among children
A．Some children start to smoke out of curiosity. B．Many children start to smoke because they want to appear mature. C．In order to have fewer children smokers, parents, teachers and health care workers should not smoke. D．It is not as difficult to prevent children from starting to smoke as to persuade adults from smoking.
A．folded B．folding C．twisted D．twisting