To a worker, ________ from the point of view of society is necessary labor is from his own point of view voluntary play.
正确答案： A
本题解析：
本题要求填入一个关系代词引导主语从句，并在主语从句中作主语，所以选 what。
The wounded soldiers would recover quickly if they were well ________.
_______ at all is worth doing well.