A:Did you climb to the top of the Statue of Liberty when
you were in New York?
B:No,I didn't. My knee was very sore,and I____climb all those stairs.
(a)might (b)couldn't (c) must not
這題must not 為什麼不能用?

You must not talk. 你絕對不能（不准）說話。怎麼可能是用它咧？助動詞就幾個而已，每個的意思其實差蠻多的，多看幾遍，多找例句吧！

其實也我知道他意思不一樣啦，因為課本有說他還有邏輯跟否定的意思，所以我才在想說 他是否能選