Input: Article: Hydrogen gas was first artificially produced in the early 16th century, via the mixing of metals with acids. In 176681, Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance, and that it produces water when burned, a property which later gave it its name: in Greek, hydrogen means "water-former".

Now answer this question: When was hydrogen gas artificially produced for the first time?

Output: early 16th century

Input: Article: As is known from the "Sumerian Farmer's Almanac", after the flood season and after the Spring Equinox and the Akitu or New Year Festival, using the canals, farmers would flood their fields and then drain the water. Next they made oxen stomp the ground and kill weeds. They then dragged the fields with pickaxes. After drying, they plowed, harrowed, and raked the ground three times, and pulverized it with a mattock, before planting seed. Unfortunately the high evaporation rate resulted in a gradual increase in the salinity of the fields. By the Ur III period, farmers had switched from wheat to the more salt-tolerant barley as their principal crop.

Now answer this question: Why did the Sumerian farmers make their oxen stomp the ground?

Output: kill weeds

Input: Article: Marvel earned a great deal of money and recognition during the comic book boom of the early 1990s, launching the successful 2099 line of comics set in the future (Spider-Man 2099, etc.) and the creatively daring though commercially unsuccessful Razorline imprint of superhero comics created by novelist and filmmaker Clive Barker. In 1990, Marvel began selling Marvel Universe Cards with trading card maker SkyBox International. These were collectible trading cards that featured the characters and events of the Marvel Universe. The 1990s saw the rise of variant covers, cover enhancements, swimsuit issues, and company-wide crossovers that affected the overall continuity of the fictional Marvel Universe

Now answer this question: What was affected by the increasing use at Marvel of crossover stories between comic characters?

Output:
overall continuity of the fictional Marvel Universe