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The S&P 500 (SNPINDEX:^GSPC) had yet another impressive month in November, climbing by almost 3% and helping it jump well over 10% just since the beginning of September. Investors have gotten increasingly optimistic about the stock market's ability to weather the coming storms from Fed tapering and federal-government shenanigans, and they've pushed more than 90% of the stocks in the S&P 500 up so far this year. Yet among the top performers, Tesoro (NYSE:TSO), Micron Technology (NASDAQ:MU), Biogen Idec (NASDAQ:BIIB), and First Solar (NASDAQ:FSLR) climbed the most in November. Let's take a closer look at those four stocks to find out why they crushed it last month.

Tesoro soared 20.4% in November, recovering from a period of weakness for the refinery industry in general. The spread between prices of domestic West Texas Intermediate crude and global Brent crude widened considerably last month, reversing a troubling trend that had seen the spread almost entirely disappear briefly during the summer months. Tesoro's refinery locations let it take advantage of this spread, with less expensive crude coming from the Bakken region to help it bolster its profits. Those favorable trends could continue as long as spreads remain high.

Micron Technology climbed 19.3% last month, adding to gains that have seen the semiconductor-maker's stock more than double since May. Micron has assumed a much larger role in the memory-chip industry since the completion of its takeover of Japan's Elpida, taking maximum advantage of the rebound in demand for memory products. Moreover, a new architecture for its processors could help Micron stand out from its rivals despite the intense competition that has plagued the memory space for years.

Biogen Idec posted a 19.2% gain in November, with the bulk of the gains coming late in the month. The Committee for Medicinal Products for Human Use, Europe's primary regulatory body for drug approval, said that Biogen's multiple sclerosis drug Tecfidera qualified for the lucrative new-active-substance designation, which will give Biogen extra time to enjoy patent exclusivity. With sales of the drug already having ramped up significantly, investors are looking at Tecfidera as a potential blockbuster, and that's making shareholders more enthusiastic about the stock's potential in the long run.

First Solar finished last month with an 18.9% rise, and by contrast to Biogen, almost all of its gains came early in November after the solar giant's earnings report. Results included a more than 50% jump in revenue, with net income doubling and the company raising earnings guidance for the full year. Favorable backlog figures and growth in gross margins reassured investors that First Solar is moving in the right direction. The stock has backed away from its biggest gains of the month as some investors fear the rising popularity of residential-solar projects, in which First Solar has played a minimal role compared to some of its rivals. But with its successful utility-scale focus, First Solar continues to dominate its niche.

The gains these four stocks have enjoyed are no guarantee that they'll keep climbing. But as long as the favorable conditions that helped them rise stay in place, they could keep helping the S&P 500 climb to new records this month and throughout the coming year.

Fool contributor Dan Caplinger and The Motley Fool have no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.