-What are you doing?
-I'm ____ a book. [ ]
A. read
B. reading
B
某天，南京市的最低气温是零下2摄氏度，记作-2℃；广州市的最低气温是零上20摄氏度，记作______℃．
血浆运送的Vit D型式是
A．7-去氢胆固醇
B．1.25(OH)2-D3
C．25(OH)D2
D．以上皆非
