根据汉语意思完成句子。
1. The cost is 50 yuan__________ _________ (每人).
2. We will take the bus _________ _________ _________ (一路上) to the museum.
3. If you want to come, please let me know________ ________ ________ ________ (尽快).
4. We should _________ __________ _________ __________ __________(保密).