He _______ computer games when his parents left home. So he didn't know where they were.
A:is playing
B:plays
C:played
D:was playing
中考前小明的午餐食谱是:主食﹣﹣面包;配菜和副食﹣﹣炸鸡腿、米饭、牛排、牛奶.则该午餐食谱缺乏的营养素是( )
71与19的最大公约数是( )