液压系统压力低或无油压原因有哪些?
参考答案:
⑴油泵内泄或油泵坏;
⑵联轴器键滚;
⑶吸油管漏气或堵塞;
⑷油箱油面太低;
⑸液压油粘度大;
⑹系统溢流阀阀芯卡阻
11个月小儿,人工喂养,户外活动少,未规律添加维生素D,今日突然发生手足肌肉痉挛,手腕屈曲,手指僵直,踝关节僵直,足趾弯曲向下。则患儿的血清总钙至少低于()。
A.1.0mmol/L
B.1.38mmol/L
C.1.88mmol/L
D.2.25mmol/L
E.2.7mmol/L
His name is James, but he calls _____ Jim. [ ]
A. his
B. himself
C. him
D. /