---enough time ,we did not finish the work

你的句子是表明原因的独立主格结构.变成原因状语从句就是：As there was not enough time,we didn't finish the work.或者：There was not enough time,so we didn't finish the work.就是说,如果选D,句子里必须要有as / so这样的连接词来连接前后两句.
又如：As Mike has fallen ill,I have to finish his part of the work(这是原因状语从句)请你变成独立主格结构：
Mike having fallen ill,I have to do his part of the work.