Though it is 30 years___we last met,I still remember the sce

第一个空填since 是自从的意思,第二个空是定语从句,修饰scene,用where引导,指地点,在定语从句中作状语,即
Though it is 30 years since we last met,I still remember the scene where we got seperated on a rainy day.
翻译：尽管自从我们上次见面,30年过去了,但是我仍然记得我们在雨天分离的场景.
如果用before 在句中意思不通,是说我们上次见面之前30年,句意不符；第二个空不是修饰时间,而是修饰的scene,所以不用when引导
有不明白的请继续追问,