According to the passage, the statement that best describes the writer's attitude is ______.
A. there are no ways to make workers more productive
B．workers want more variety, freedom and money, but shorter working time and less contribution
C．variety, freedom, contribution, more money and shorter working time seem possible factors leading to greater productivity, actually they are not or they are impossible
D．it is impossible to make workers work more productively, because the work they do is so boring