见补充—When was it that you got to know Jack?—Let me see.Maybe

不懂的别乱说
首先问句中强调句重点问时间
答句中要回答when 答案用when 不是强调句,是定语从句,解释先行词 in the 1990s
单独第二句可以填that看做强调句,但意思是 就是在20世纪90年代我们在在小学. 答案是 就是在20-90年代,当时我们在在小学. 填that答非所问.犹如
where was it that you found your bag? 你到底在哪找到你的包的?
it was in the room where i lived last night.在我昨天住的房间里
it was in the room that i lived last night 昨天晚上我就是住的那房间