C）根据对话内容，从下面方框中选择适当的单词或短语填空，使对话内容完整正确。

Tom： I give up! I____ can't learn English!
Amy:  Why do you say that? I think you are making a lot of____ .
Tom:  No, I'm not. I try and try and I still can't speak it very well.
Amy:  Learning any language ____  a lot of effort. Please don't give up.
Tom:  Amy, I know you always____ English. Can you offer me some valuable advice?
Amy:  Listening to English tapes and watching English movies may be helpful. But always remember your English will improve if you are really____ it.
Tom:  Good idea. I will try to love English.

市场上有一种“55℃保温杯”，外层为隔热材料，内层为导热材料，夹层间有“神奇物质”。开水倒入杯中数分钟后，水温降为55℃且能较长时间保持不变。“神奇物质”在55℃时（   ）