怎么理解B选项 兼职的人在增加

问题如下：

Over the last few decades, developed countries have most likely experienced declining:

选项：

A.average annual working hours.

B.levels of part-time employment.

C.proportions of employees with higher education.

解释：

A is correct. OECD studies indicate that most developed countries have experienced declining average working hours over the past few decades. Over the same period, part-time employment has increased as has the proportion of employees with higher education. While the number of average working hours has decreased, the average level of education has increased. The percentage of employees with a higher education degree has grown over the last few decades.