钱文宇
4. Find a seven-letter word made up of only the four following letters：
O， N， I， P
5. Find a word which， when placed in the brackets， forms two different words with the letters eachside. GR （..） TO
6. I am nine-letter long：
123456-789. My first four “1234” is to recognize. My last five “56789” is a ridge. My last four “6789” is a boundary. What am I？