单项选择题
A．because they took place at night B．as a signal for the crowd together C．to limit the time when offers could be made D．to keep the auctioneer warm
A．are yet to be proved B．are to be further studied C．are supported by scientific evidence D．are self-evident
A．the Apollo mission was very successful B．protection from space radiation is no easy job C．astronauts will have deformed children of grandchildren D．radiation is not a threat to well protection space explorers