By the middle of the 20th century scientists believed they were well on the way to treating, preventing, or eradicating many of the deadly infectious diseases that had plagued humankind for centuries.为什么句中用了 that 没有用 those 呢,指代的不是复数吗?
一道单选题:The government is to end the system _____ farmers make more money by leaving land unplanted than by growing rice.填 that。是同位语从句还是填 in which 成为定语从句?