火箭在大气中飞行时，它的头部磨擦发热，温度可达几千摄氏度。在火箭上涂一层特殊材料，这种材料在高温下熔化并且汽化，能起到保护火箭头部的作用，这是因为（    ）

增加: 在缺词处加一个漏字符号(/\),并在其下面写出该加的词。

删除: 把多余的词用斜线(\) 划掉。

修改: 在错的词下划一横线，并在该词下面写出修改后的词。

注意: 1）每处错误及其修改均仅限一词:

2）只允许修改10处，多者(从第11处起) 不计分。

    Mr. Johnson is a hardworking teacher. Every day, he spends too much time with his work. With little sleep and hardly any break, so he works from morning till night. Hard work have made him very ill. “He has ruined his healthy. We are worried about him.” That is which other teachers say. Yesterday afternoon. I paid visit to Mr. Johnson. I was eager to see him, but outside her room I stopped. I had to calm myself down. Quietly I step into the room. I saw him lying in bed, looking at some of the picture we had taken together. I understood that he missed us just as many as we missed him.

在“百度”搜索引擎中输入“1955年、周恩来、求同存异”几个关键词，你可以搜索到哪次会议的相关内容（    ）