remain这里是系动词,remain to be done 是有待于去做,本句中使用remaining 现在分词短语做定语.
如： With many problems remaining to be done, he can't spare time for a holiday.
还可说： remain silent
remain standingremain seated
remain the best of friendsremainto been seen现在分词做定语，remain是系动词，那系动词怎么有现在分词形式呢系动词有现在分词比如： There are many flowers smelling sweet in the garden.系动词的非谓语动词形式只有现在分词，没有过去分词