有关孕激素的生理作用正确的是
A.促进乳腺管发育
B.促 * * 上皮角化,糖原增加
C.使子宫肌肉对缩宫素的敏感性增强
D.使宫颈黏液拉丝度加大
E.促使宫颈口闭合
参考答案:E
饲养试验
As for most students, they find it very difficult ______ English well. [ ]
A. to learn
B. learning
C. learn