请教各位大虾下面这道题目为什么是D啊？

既然两个公司都很少出现加班现象，那为什么会发生Y的计时工资比Z高呢？

Which of the following most logically completes the argument?

Yorco and Zortech are two corporations that employ large numbers of full-time workers who are paid by the hour. Publicly available records indicate that Yorco employs roughly the same number of such hourly wage workers as Zortech does but spends a far higher total sum per year on wages for such workers. Therefore, hourly wages must be higher, on average, at Yorco than at Zortech, since _____.

Zortech spends a higher total sum per year than Yorco does to provide its hourly wage workers with benefits other than wages

the work performed by hourly wage workers at Zortech does not require a significantly higher level of skill than the work performed by hourly wage workers at Yorco does

the proportion of all company employees who are hourly wage workers is significantly greater at Yorco than it is at Zortech

overtime work, which is paid at a substantially higher rate than work done during the regular work week, is rare at both Yorco and Zortech

the highest hourly wages paid at Yorco are higher than the highest hourly wages paid at Zortech

Answer: D