your homework ( ) by the time i come back

选择D is to be done
先说初中阶段涉及到的六种时代的被动语态：
一般现在时：is done
一般过去时：was done
一般将来时：will be done; am/is/are going to be done; is to be done
现在进行时：am/is/are being done
过去进行时：was/were being done
现在完成时：have/has been done
所以先排除选项A is to being dome 和C is to been done。
再看题目by the time I come back,是表示将来的时间,因为是时间状语从句,所以用一般现在时。
所以主句应该用一般将来时,只能选择D is to be done。
意思是：到我回来的时候,你的作业要做完。