Question

2007年专升本真题中选择题第50题的C选项何解？

He grew more and more absorbed in his work ,_____he almost forgot his meals.
A. that to such an extent
B. to an extent such that
C. to such an extent(天一教材) to such an extent that (云飞教材)
D.such that to an extent
在云飞书中C选项是to such an extent that，而在天一书中是，在云飞书中是to such an extent,有谁能告诉我真题到底是怎样的，又如何解释呢？

Answer 1

因为是定语从句，that 是用来修饰 extent 。可以省略的