阅读诗歌回答后面小题。
                                                                                                              跌 倒
                                                                                                              牧 也
                                                                                                       风，跌倒了
                                                                                                      才有了美丽的落叶
                                                                                                      云，跌倒了
                                                                                                      才有了滋润大地的雨水
                                                                                                       所以
                                                                                                       我们不再害怕跌倒
                                                                                                       让我们在跌倒时
                                                                                                       用最美丽的姿势
                                                                                                        站起来

中学生小陈喜欢英语，他和同学要一起参加全国英语比赛，但所在学校只有一个参赛名额。在学校的英语比赛中，为争得名额，他生怕别人超过自己，看到别人的精彩之处，他难过得晚上都睡不着觉。对于他的这种心理，正确的理解是(   )

写出空缺处各单词的正确形式，每空只写一词。

It is amazing that a cow has four ____ (胃).

方程x+2y=5的正整数解的个数为（　　）