They have made much progress__(用）their hard work. 这个“用”,是“以.的方法”,with 如：With the help of the computer we can do lots of things. 用了电脑,我们可以做许多事（在电脑的帮助下） by也可以是“以...”、“通过...”,by doing更常用,with sth.更常用 本句中their hard work是个名词,所以用with比by更好 但如果是asking often and learning,就用by更好
