When deeply absorbed in work he often was he would forget all about eating or sleeping.

问题补充：

When deeply absorbed in work, he often was, he would forget all about eating or sleeping.

A. that

B. which

C. where

D. when

答案：

A. that

(答案→)B. which

C. where

D. when

解析：考察定语从句（非限定性）。本题主句部分完整，且选项包含that, which因此在考查定语从句。应先分析空格之后的句子成分，本题缺少was的表语，且空格前有逗号，应选which。句意：当他集中精力工作时，这种情况常有发生，他总是废寝忘食。