过期妊娠对母儿的影响不包括（） A.胎儿窘迫增加 B.肩难产率增加 C.新生儿胎粪吸

甲厂向乙厂发出要约，推销磁粉。乙厂给甲厂答复：同意甲提出的其他条件，但磁粉价格须每吨降低150元，乙厂的这一答复属于( )。

A．要约

B．要约引诱

C．承诺

D．附条件承诺

输油臂的动作缓慢原因之一是（）。

A、臂中有液体

B、转子损坏

C、液压系统进气或泄漏

D、滚珠轴承磨损

残气量及残气量/肺总量比值明显增加见于（）。

A.肺部炎症

B.肺部纤维化

C.阻塞性肺气肿

D.胸腔积液

E.气胸

A definite advantage of using water as a fire extiguishing agent is its characteristic of（）.

A.alternate expansion and contraction as water in a liquid state becomes a vapor

B.absorption of smoke and gases as water is converted from a liquid to a vapor

C.rapid contraction as water is converted from a liquid to a vapor

D.rapid expansion as water absorbs heat and changes to steam

胚层形成于胚胎发生的第几周？