z指代When deeply absorbed in work
which可指代前面整句話的內(nèi)容,這是語(yǔ)法規(guī)則.When deeply absorbed in work這一句好像少了成分，為什么可以這樣省略=When he is deeply absorbed in work
英語(yǔ)中，過(guò)去分詞作狀語(yǔ)時(shí)，有時(shí)為了使條件、時(shí)間等一目了然，可以在分詞前加when/while/if/unless等，往往可轉(zhuǎn)換成一個(gè)從句，由于過(guò)去分詞表被動(dòng)，所以，從句為被動(dòng)語(yǔ)態(tài)。
祝你進(jìn)步！應(yīng)該＝When he was deeply absorbed in work,
因?yàn)閣hich_ he often was是過(guò)去式，對(duì)吧when he is/ was...均可