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。
Betty is a good friend of m________. We often help each other.
They have invited a_________(science) to give them a speech on space.
Mrs. Chan told us to write as_________(care) as we could.
We Chinese sometimes__________(借) words from English when talking.
Victor__________(敲) the door before he walked into the room.