题目

My 23-year-old son Dan stood in the doorway, ready to say goodbye to his home．In a couple of hours he was going to fly out to France．He was going to be away for at least a year to learn a foreign language and __1__ life in a foreign country．        It was a milestone in Dan’s life, a change from school days to   2  ．When we were to say goodbye, I   3   closely at his face．I would like to provide him with good   4_  that would last longer than here and now．        But not a sound came over my lips．I   5  motionless and silent, looking    6__my son’s导致“温室效应”的原因是人类向大气中排放大量的（　） A．CO　　　　　　　　   B．CO2　　　　　　    C．NO2　　　　　　    D．SO2