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.