短文改错。

     Last summer I learnt to ride a bicycle. At first,I was unable to control it's direction. Sometimes

I fall to the right or to the left. But I asked my father to tell me how I could ride straightly. He didn't

answer me directly. Instead, he took me to side of the street. "Can you find some bike track that is

really straight?" asked my father. I watched more carefully and shook my head ."No" he said, "in fact

neither of the tracks is always straight. But just by correct the direction every now and then, you had

already gone forward."

子宫脱垂最主要的病理改变是（）

A.圆韧带变厚

B.圆韧带松弛

C.骨盆漏斗韧带松弛

D.宫骶韧带松弛

E.盆底组织松弛，失去正常张力