People faint (晕) when the normal blood supply to the brain is suddenly cut down. This can happen if they are surprised or shocked by sudden news or by something they see. Some people faint if they see others hurt. Some people faint in crowds. Others faint if they are in a room that is hot and with all the windows closed. If a person faints while standing, lay him down. If his face is pale, lift his feet. If he is sitting down when he faints, place his head between his knees. Loosen any tight clothing that might keep him from breathing easily. If possible, place cold, wet cloth on his forehead. We try to help a person who has fainted by______.
A．rubbing his head B．returning blood to his brain C．tightening his muscles D．holding him in an upright (垂直) position