It's nature that sb should do ...nature可以换成决定、主张、要求、建议、命令等词,

此处应该是形容词natural吧?
已经很全了
1在表示建议、要求、命令的动词之后引导的宾语从句要虚拟
结构：主1+vt+that+主2+(should)do
表建议：suggest/advise/recommond/propose
表命令：order/command
表要求：require/request/demand/insist（坚持要求）/desire愿望(此处意思为要求、命令,不是)/ask
其他：prefer宁愿
eg.They insisted that the boy (should) go with them.
2主语从句中虚拟语气It is +done/adj +that+主+(should)do
done是指情况1中动词的过去分词如：suggested 等
adj有：necessary/important/strange/natural/essential
eg.It is suggested that the meeting (should)be put off till next week.
eg.It is strange that he (should) have acted toward his parents like that.
3表语从句和同位语从句中的虚拟语气
...n+that+主+(should)do
名词有：suggestion/proposal/order/plan/idea/request/advice等
eg.We all agree to his suggestion that we (should) go to Dalian for sightseeing.