lest ,in case ,for fear that虚拟语气后从句用should/would /could/migh

lest ,in case ,for fear that虚拟语气后从句用should/would /could/might+do的区别
While crossing the mountain area,all the men carried guns lest they __by wild animals.
would be attracked /should be attracked
Tmad man was put in the soft-padded cell lest he would injure himself.(1997.12.CET4)
这题A.injure为什么不行
有语法书上说lest ,in case ,for fear that虚拟语气后从句用should do,in case 后should不可省,lest ,for fear that后should可省