If there is a lot of work ．I’m happy to just keep on until it is finished．
A. to do
B. to be doing
C. done
D. doing
网友回答
(答案→)A. to do
B. to be doing
C. done
D. doing
解析： 此处to do在句中做定语修饰work，本句的意思是：如果有很多工作要做，我很乐意一直把它做完。【点拨】不定式做定语往往表示未发生的动作，放在被修饰词的名词、代词后。