根据下列句子的意思及所给的汉语提示，写出空缺处单词、固定短语或固定搭配的正确形式。
1. Betty is a good friend of m________. We often help each other.
2. They have invited a ________ (science) to give them a speech on space.
3. Mrs. Chan told us to write as ________ (care) as we could.
4. We Chinese sometimes ________ (借) words from English when talking.
5. Victor ________ (敲) the door before he walked into the room.
