Which of the following statements is TRUE about the sentence “When deeply absorbed in work, which he often was, he would forget all about eating and sleeping.”?
A、The part “which he often was” is a restrictive attributive clause.
B、The part “which he often was” is a non-restrictive attributive clause.
C、It is best translated into “当聚精会神工作的时候（他常常这样），他会忘了吃饭和睡觉。”.
D、It is best translated into “当他经常聚精会神工作的时候，他会废寝忘食。”.
A、The part “which he often was” is a restrictive attributive clause.
B、The part “which he often was” is a non-restrictive attributive clause.
C、It is best translated into “当聚精会神工作的时候（他常常这样），他会忘了吃饭和睡觉。”.
D、It is best translated into “当他经常聚精会神工作的时候，他会废寝忘食。”.