I was not satisfied with the answers given to this question and others, so I decided to type my own answer. Hope you like it! :)
a) Identify ONE specific example of how historians might argue that the end of the Cold War was attributable to Reagan’s policies and US pressure.
Ronald Reagan was a huge factor in ending the Cold War, as he negotiated with Soviet President Mikhail Gorbachev numerous times, building up a friendship while working on the sidelines to end the Cold War. Besides negotiating, Reagan "developed a broad counteroffensive strategy. He initiated a $1.5 trillion military buildup, the largest in American peacetime history, which was aimed at drawing the Soviets into an arms race he was convinced they could not win. He was also determined to lead the Western alliance in deploying 108 Pershing II and 464 Tomahawk cruise missiles in Europe to counter the SS-20s. At the same time, Reagan did not eschew arms control negotiations. Indeed, he suggested that for the first time the two superpowers drastically reduce their nuclear stockpiles" (historynet.com). The fact that Ronald Reagan negotiated treaties to de-escalate the rising threat of a nuclear war gives a great example of how the end of the Cold War was attributable to Reagan’s policies and US pressure.
b) Identify ONE specific example of how historians might argue that the end of the Cold War was attributable to Gorbachev’s leadership.
While Mikhail Gorbachev "is not popular with the Russian people who blame him for the loss of Soviet power" (belfercenter.org), the end of the Cold War was attributable to Gorbachev’s leadership due to the actions the former Soviet President took. "Ultimately, the deepest causes of the Soviet collapse were the decline of communist ideology and economic failure. This would have happened even without Gorbachev. In the early Cold War, communism and the Soviet Union had considerable soft power. Many communists led the resistance against fascism in Europe and many people believed that communism was the wave of the future" (belfercenter.org).
c) Identify ONE reason (other than partisanship), based on the events of the last decade of the Cold War, that historians might still debate the respective influences of Reagan and Gorbachev on the end of the Cold War.
The respective influences of Reagan and Gorbachev on the end of the Cold War are widely debated by American People long after the end of the Cold War for differing reasons.  Many people directly involved are still asking: Was Soviet communism defeated? Was it overthrown? Or did it simply collapse from within? Many people across the globe question whether Reagan "won" the war or not. Michael Cox, a British professor, asked his students a simple question regarding the Cold War: "Indeed, in a recent class I taught at my home institution—the London School of Economics—I asked a simple question about which policy-maker at the time was most instrumental in ending Soviet control in Eastern and Central Europe. Reagan was of course high on my list of possible candidates; and you might say that for a European I made a fairly strong case for him—but to no avail. Amongst a group of 500 very bright first-year students, there seemed to be only one correct answer, and that was not Ronald Reagan but, rather, Soviet leader Mikhail Gorbachev. By a considerable margin it was the Russian rather than the American who won the overwhelming majority of votes (over 70 percent of the total)" (ap.gilderlehrman.org), showing that there is still debate on the respective influences of Reagan and Gorbachev on the end of the Cold War.
