The plan is perfect and I see no reason to _______ that it isn’t working

　　 仔细阅读下面五个句子，然后用下面方框中所给的单词或短语填空，使每个句子在结构、句意和逻辑上正确。（提示：选项中有一个是多余的。）
　　46. The plan is perfect and I see no reason to _______ that it isn’t working.
　　47. Remember to use _______ chopsticks for meats， vegetables and salads.
　　48. A pizza and a cake？ That’ll be _______ for us， unless you are very hungry.
　　49. I think maybe I could _______ such a house if I work really hard for the rest of my life.
　　50. Many animals in Africa are in danger， and people are making plans to _______ the animals.
　　46. _________ 47. _________ 48. _________ 49. _________ 50. _________