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.”?<br/> A、The part “which he often was” is a restrictive attributive clause.<br/> B、The part “which he often was” is a non-restrictive attributive clause.<br/> 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。”.<br/> 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。”.