TASK DEFINITION: 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.
PROBLEM: 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?

SOLUTION: is arbitrary

PROBLEM: Passage: Under the 1963 constitution, Massamba-Débat was elected President for a five-year term. During Massamba-Débat's term in office the regime adopted "scientific socialism" as the country's constitutional ideology. In 1965, Congo established relations with the Soviet Union, the People's Republic of China, North Korea and North Vietnam. Massamba-Débat's regime also invited several hundred Cuban army troops into the country to train his party's militia units and these troops helped his government survive a coup in 1966 led by paratroopers loyal to future President Marien Ngouabi. Nevertheless, Massamba-Débat was unable to reconcile various institutional, tribal and ideological factions within the country and his regime ended abruptly with a bloodless coup d'état in September 1968. Question: What was a term that could describe the political philosophy of the Congo under Massamba-Debat?

SOLUTION: scientific socialism

PROBLEM: Passage: Development of a solar-powered car has been an engineering goal since the 1980s. The World Solar Challenge is a biannual solar-powered car race, where teams from universities and enterprises compete over 3,021 kilometres (1,877 mi) across central Australia from Darwin to Adelaide. In 1987, when it was founded, the winner's average speed was 67 kilometres per hour (42 mph) and by 2007 the winner's average speed had improved to 90.87 kilometres per hour (56.46 mph). The North American Solar Challenge and the planned South African Solar Challenge are comparable competitions that reflect an international interest in the engineering and development of solar powered vehicles. Question: What is The World Solar Challenge?

SOLUTION:
a biannual solar-powered car race