A、<span style="font-size:14px;font-family:宋体;color:#222222">长度法和系数阻力法</span>
B、<span style="font-size:14px;font-family:宋体;color:#222222">当量长度法和阻力系数法</span>
C、<span style="font-size:14px;font-family:宋体;color:#222222">当量法和系数法</span>
D、<span style="font-size:14px;font-family:宋体;color:#222222">长度法和阻力法</span>