Yesterday Mary couldn't finish her homework,so she has to go

Yesterday Mary couldn't finish her homework, so she has to go on (with) it this afternoon.
Yesterday Mary couldn't finish her homework, so she has to go on (doing) it this afternoon.
如果选项是to do与doing,则要选择doing,继续做同一件事
如果是继续做另一件事,可以用go on to do
After I finished my home work, I went on to play with my friends.
我完成作业后,继续和朋友们玩.

she has to go on with it.

do housework 、go no doing something .所以这里要用doing 了。

go on to finish

doing
解释：go on doing it 表示“继续做家庭作业”。
祝你新年快乐，学习更上一层楼！请记得采纳，谢谢！(*^__^*)