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.