单项选择题A．Whether second hand smoking is liked with cancer.B．Whether active smoking is linked with cancer.C．Whether passive smoking by children is liked with childhood cancers.D．Whether an average degree of passive smoking is harmful.

单项选择题A．It doesn’’t need to be refueled.B．It will use solar energy as fuel.C．It will be driven by electrical power.D．It will be more suitable for long distance travel.