Very few people have to finish the work before going home,  _________ ?       [ ]

A. have they    

B. do they        

C. don't they  

D. haven't they

29岁初产妇，妊娠39周，规律宫缩9h入院。体检：髂棘问径24cm，骶耻外径19cm，坐骨棘间径10cm，坐骨结节间径7.5cm；枕左前位，胎心140次/分。肛查宫口开大4cm，S=0。2h后产妇呼叫腹痛难忍，检查宫缩1min一次，持续40s，宫缩时胎心116次/分，子宫下段压痛明显。 * * 检查宫口开大5cm，先露为胎头。

此时产程受阻的原因主要是

A．骨盆入口狭窄
B．骨盆出口狭窄
C．中骨盆狭窄
D．扁平骨盆
E．漏斗骨盆