think and write

think and write
1) hospital - low - ___ - ___ - kitchen - ___ - ___
2) museum - ___ - ___ - ___ - ___
3) onion - ___ - ___ - ___ - ___
这道题应该从哪方面想呢?我找不出有什么必然联系,
一定要解释从哪方面想得，不应该很难得，