Whatever is left over may be put into the refrige

Whatever is left over may be put into the refrigerator, _________ it will keep for two or three weeks.
请详细分析一下，横线上为什么填where, 请说明一下理由，十分感谢。

keep在这里是不及物动词，用作说明食物的保存

it will keep for two or three weeks，where=in the refrigerator whatever is left over may be put into the refrigerator，但我认为which也可以，可以理解为it代指the refrigerator，which代指whatever is left over ，keep为及物动词，能不能？ 不能填which.中的主语是it ，此句缺少【地点状语】whatever is left over may be put into the refrigerator, _____ it will keep for two or three weeks. 我知道空可以填where。因为which是关系代词，关系代词在定语从句中做主语或宾语, where it will keep for two or three weeks.=whatever is left over may be put into the refrigerator, and it will keep for two or three weeks in the refrigerator