问题
选择题
When deeply lost in thought, _______ he often was, he would forget all about eating or sleeping.
A．that
B．where
C．which
D．when
答案
答案：C
题目分析:考查定语从句。由结构判断此处是定语从句，从句缺少表语，用关系代词，故排除B、D选项， 而that不引导非限制性定语从句，所以答案选C。句意：当他陷入沉思中时，他总会忘记吃饭、睡觉，这种情况时常发生。