72．What is mainly described in the passage ? (A)．A historic discovery . (B)．An event of imagination (C)．A research on space . (D)．A scientific adventure .

74．Why can’t the northern half of the earth escape for long ? (A)．Because the land is covered with water (B)．Because the light and heat from the sun can not reach the earth . (C)．Because people there can not live at the temperature of zero . (D)．Because wars break out among countries .