The War on Drugs is controversial. Tell me if you agree with the current War on Drugs or disagree with it. If you agree tell me a well explained reason why. If you disagree propose a better approach to dealing with drug addiction, abuse and crime.

the fourth alternative is correct (d).

all of these alternatives can be used. when we are talking about something that happened in the past, it is not easy to remember precisely the date it occurred. thus, we can use the beginning / end of a century or decade or some striking event that has occurred close to and is of wide knowledge. this is a way to reference the time for the interlocutor to contextualize it.