Sentence Correction

In the 1960s, to reduce the discharge of untreated wastes into the Great Lakes, limits were set by the United States and its neighbouring countries on the amount of effluents that could be discharged into these water bodies
ï‚· limits were set by the United States and its neighbouring countries on
ï‚· limits set by the United States and its neighbouring countries for
ï‚· the United States and its neighbouring countries have set limits on
ï‚· limits have been set by the United States and its neighbouring countries restricting
ï‚· the United States and its neighbouring countries set limits on
OA : E Why not C

It is not C because it happening in the 1960s. 'Have set' is in the present perfect as you mention, meaning it is the wrong tense for something that already happened.

Good day instructors,
Just as the asker said, I'm also confused regarding the use of set instead of have set
for me the Present perfect use is still correct as it referes to something that happend in the past and its consequences are still going on in the present
the limits haves been set in the past but their effects are still up-to-date
Please help with point
thanks

They are up to date, but the question is when were the limits set? In the past.

Yes the limit was set in the past but it's effect is still there. So, why not present perfect. I am also confused. This is a really confusing topic. I also chose C as my answer choice. Anyone, please explain the concept properly, like what are the indicators through which we can definitely say that yes in this simple present tense will be used and not the present perfect tense.

You wouldn't use a present tense because the sentence begins with "In the 1960s." If the limits were continuing to be set, the sentence would begin "Since the 1960s, countries have set limits." It's a past action, not a continuing one, so C is not correct.