A:图线A是电阻R1的I﹣U关系图象
B:电源电压为18V
C:R1的阻值是20Ω
D:滑动变阻器R2的最大阻值为70Ω
Are these his shoes? No, they____ (aren't/are).
培养细菌和真菌的____ 和____ ,在接种前必须____ 。