求助！有关定语从句的几个问题~ 急~ 求详细解释，谢谢！

求助！有关定语从句的几个问题~ 急~ 求详细解释，谢谢！
1.请帮我翻译一下这句句子：As can be seen from the comparison of these figures,the principle involves the active participation of the patient in the modification of his condition.
2.The death of her husbandand the suffering ______ caused affected the young lady greatly.
A.that B.it C.what D.which
3.The biggest single hobby in western countries _____ western people spend their most time,energy and money is gardening.
A.in which B.where C. that D.on which(这道题为什么不选B?)
4.The mayor will make an inspection of our school on Monday ,____ you can tell him how hard a situation we are in.
A. where B.which C. when D.that(这题为什么不选A？）