This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

Passage: Though researchers generally believe that sexual orientation is not determined by any one factor but by a combination of genetic, hormonal, and environmental influences, with biological factors involving a complex interplay of genetic factors and the early uterine environment, they favor biological models for the cause. They believe that sexual orientation is not a choice, and some of them believe that it is established at conception. That is, individuals do not choose to be homosexual, heterosexual, bisexual, or asexual. While current scientific investigation usually seeks to find biological explanations for the adoption of a particular sexual orientation, there are yet no replicated scientific studies supporting any specific biological etiology for sexual orientation. However, scientific studies have found a number of statistical biological differences between gay people and heterosexuals, which may result from the same underlying cause as sexual orientation itself. Question: What do researchers generally believe causes sexual orientation?
a combination of genetic, hormonal, and environmental influences

Passage: In Chapter II, Darwin specifies that the distinction between species and varieties is arbitrary, with experts disagreeing and changing their decisions when new forms were found. He concludes that "a well-marked variety may be justly called an incipient species" and that "species are only strongly marked and permanent varieties". He argues for the ubiquity of variation in nature. Historians have noted that naturalists had long been aware that the individuals of a species differed from one another, but had generally considered such variations to be limited and unimportant deviations from the archetype of each species, that archetype being a fixed ideal in the mind of God. Darwin and Wallace made variation among individuals of the same species central to understanding the natural world. Question: What does Darwin believe about the differences between species and varieties?
is arbitrary

Passage: With the introduction of the blast furnace to Europe in the Middle Ages, pig iron was able to be produced in much higher volumes than wrought iron. Because pig iron could be melted, people began to develop processes of reducing the carbon in the liquid pig iron to create steel. Puddling was introduced during the 1700s, where molten pig iron was stirred while exposed to the air, to remove the carbon by oxidation. In 1858, Sir Henry Bessemer developed a process of steel-making by blowing hot air through liquid pig iron to reduce the carbon content. The Bessemer process was able to produce the first large scale manufacture of steel. Once the Bessemer process began to gain widespread use, other alloys of steel began to follow. Mangalloy, an alloy of steel and manganese exhibiting extreme hardness and toughness, was one of the first alloy steels, and was created by Robert Hadfield in 1882. Question: What did the blast furnace help do to pig iron in the middle ages?

produced in much higher volumes than wrought iron