...5.这题的答案是would not have fallen,而我觉得是would not fall, 从句是对过去情况的虚拟倒装if the…scientists had not…,但主句用的是since+时间点,不应该是表示是从2015年到现在吗?有since的地方大都用用现在完成时,应该是指的是现在...
While the effect of cows milk harvested at different time has not been tested on humans up to now, taking melatonin drugs has been suggested to those who are struggling to fall asleep at night.请问这里的time 为什么不用复数?