Many scientific discoveries have been made by accident—while scientists were studying one thing, they stumbled upon something else entirely. One such example involves the discovery of penicillin, a powerful antibiotic that revolutionized medicine, by Alexander Fleming. While studying bacteria in 1928, Fleming left a petri dish of bacteria uncovered in a lab. When he returned, Fleming observed that a mold had grown in the dish, and that, surprisingly, the bacteria surrounding the mold had died. The discovery of penicillin provides a powerful illustration of how ______.

SAT · English · previous-year question