It was not until last week__she found-_she thought was quite

1.首先是it is/was...that...的强调句句型,强调时间：last week.这种句型的特点是如果把it is/was...that...省去,原句意思/结构不变,仍然是完整的句子.
2.然后,what是作为thought的宾语出现的.正句句子的成分分解为she found [（what she thought） was quite mistaken].[]中的是she found的宾语从句,（）中的是was quite mistaken主语从句,what表示“她认为”的内容

第一个空：It...that是强调句式，固定的只能用that
第二个空：what she thought 是后面这个从句的主语，即直到上周她才发现她所想的东西被严重的误解了

第一个空：
not … until … 句型的强调句
A. 句型为：It is/ was not until + 被强调部分 + that + 其他部分
普通句：He didn't go to bed until/ till his wife
came back.
强调句：It was not until his wife came back that h...