A.氨基酸B.食用鹽C.氨基乙酸D.糖類
A.母畜性難產(chǎn)B.產(chǎn)力性難產(chǎn)C.胎兒性難產(chǎn)D.產(chǎn)道性難產(chǎn)
A.胎兒因素B.機械性刺激C.中樞神經(jīng)和激素調(diào)控D.免疫學機理