—Yes, he is. He history for nearly 20 years.
A:teaches
B:has taught
C:is teaching
D:will teach
1600-600 3500-3000 4100-700 600+300
2700-2000 700+600 1600-400 200+800
在正常情况下,人体内尿的形成过程中,不可能出现的情况是( )