<p>In 1972, to reduce pollution in the Great Lakes, [limits having been set by the US and Canada] on the amount of phosphorus that could be discharged into Lakes Erie and Ontario</p>
<p>D) the US and Canada have set limits
E) the US and Canada set limits</p>
<p>Correct answer is E... but WHY? </p>
<p>What does "have set" imply? What does "set" imply?? Is "set" past tense here? </p>
<p>And also, how would I remodel the sentence to make the correct answer D?</p>
<p>Like: </p>
<p>"In order to reduce pollution in the Great Lakes, the US and Canada have set limits on the amount..."</p>
<p>Does that mean that </p>
<p>ANYTIME it says "In [year]..." it has to be past tense?? and there is NEVER a "have" in any sentence with "In [year]??"</p>
<p>You are correct. In sentences with actions that happened only once in the past and were not continued, we use the past simple tense. </p>
<p>To use “have set”, the action in the sentence must
*have started in the past
and
*be continuing until now.
That’s why it’s called “present continuous tense”.</p>
<p>ohh… but in the case of “setting limits” once you set limits… aren’t you done? like it only takes one day to set a limit or something, and then for all the days after that the limits are still there but you aren’t setting limits everyday… </p>
<p>so you can’t really “have set” right? cuz you can’t be continuing to be setting? </p>
<p>I was explaining the general idea of the present continuous tense (not only with the phrase " to set").
However, I think you’re correct on that it’d be illogical to say “have set” in the sense you mean. “Have set” would probably be used only in a sentence like:
“They have just set the new limits”.</p>