阅读理解 Not many of the elements occur in nature as pure substances, lying around waiting for someone to pick them up. A few do, and it is not surprising that these were known and collected for various uses in societies around the globe as far back as several thousand years B. C. Sulfur is one of those elements. It was known to burn with smelly results and have an odd appearance. Its use was probably confined to religious ceremonies. Carbon was also known since antiquity, because the charred (烧焦的) bones of animals and portions of partially burned trees consist largely of carbon in the form of charcoal. Although we don''t know all the uses primitive peoples made of charcoal, we do know that it was the key to releasing many other elements from their chemical combination in rocks. For example, if a copper-containing rock was heated in a hot fire with charcoal present, the carbon in the charcoal would combine with the other elements in the rock, leaving free metallic copper. In ways like this people were able to discover the elements copper, iron, lead, tin, and zinc, although they didn''t necessarily appreciate that these substances were elementary. They just knew that they were useful. Iron also arrived occasionally from the heavens in the form of iron-containing meteorites (陨石). Because of this, one might think that iron would have been thought of as a "heavenly" element, a gift from the gods. Instead, this honor has always fallen to the element gold. Gold doesn''t fall from the skies, but it is found in its pure state in some places. It has the unusual property of never tarnishing (锈蚀) like other metals do. Gold objects don''t rust, as iron does, nor do they turn green or black on the surface as do many other metals. The ancient Egyptians used gold for jewelry and for coins. Gold is still used for jewelry, although pure gold is too soft for this purpose. Coins and jewelry, instead, are made of alloys. These are metals made by melting two or more metals in a pot together in such a way that they dissolve in one another. Gold coins are usually 90 per cent copper. An alloy of gold and silver is called white gold.

单选题 What''s the main idea of the first paragraph?

A、 Not many elements occur in nature as pure substances, therefore ancient people wouldn''t pick them up.
B、 Ancient people found copper, iron, lead, tin and zinc very useful, although they did not consider these to be elements.
C、 Ancient people discovered elements, found them free or lying around in their natural form and put them to use.
D、 Sulfur and carbon have been used by mankind for thousands of years, but not much has been known about them.

【正确答案】 C

【答案解析】该题问的是第一段的大意，所以要对第一段有整体的把握。选项A虽然前半句是原文的首句，但后半句与原文信息相悖。选项B具有概括性，似乎是对的，但原文倒数第二句用的是“they didn’t necessarily appreciate that these substances were elementary”．所以该选项亦不对。选项C是对第一段的概括，信息准确，故为答案。选项D的信息正确，但它只是部分的具体的细节信息，不能统领全段。