阅读材料中共包含10个未完成的句子，针对每个句子中空缺部分有4个选项，请从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
One thorn（刺）of experience is worth many times of warning.
Ralph Wick was seven years old.In most things he was a fine boy，but he would cry fromtime to time.When he could not have what he wanted，he would C-31 for it.If hewas told that it would hurt him，and he could not C-32 it，he would also cry.
One day，he went with his mother into the C-33.The sun shone.The grass wascut.The flowers were starting to come out.
Ralph thought he was，for once，a good boy.A C-34 was on his face.He wished todo as he was told.Ralph helped his mother with the farm work and he was very happy.
"Now you must be tired and C-35 said his mother."Have a good rest hereand eat some cookies.I wil get a beautiful red rose for you."So his mother brought the redflower to him.When he saw his mother stil had a white rose in her hand，Ralph C-36 it.
"No，my dear，"said his mother."See how many thorns it has.You must not touch it，or you would be sure to hurt your C-37." When Ralph found that he could not havethe white rose，he began to cry，and
C-38 took it away.But he was soon very sorry.The thorns hurt his hand.It was so C-39 that he could not use it for some time.
Ralph would never C-40 this.From then on，when he wanted what he shouldnot have，his mother would point to his hand which had been hurt before.He at last learnedto do as he was told.

C-31.Which is the best one to fill in the blank？（）