【单选题】

Sulphur is one of the oldest, cheapest, and most useful minerals in the worlD、Yellowish or greenish in (1) , this odorless material is found in the earth in a crystal form. We have discovered thousands of (2) for it. For this reason, every man, woman, and child inAmerica (3) about seventy-five pounds of it each year.

Until 1900 almost all of the world’s supply of sulphur came from the Italian (4) of Sicily. Since thenAmerica has discovered how to mine its own vast supplies found in Texas and LouisianA、Spain, Mexico, and SouthAmerica are also (5) for it. (6) , we know there are trillions of tons of sulphur in our oceans.
In Sicily sulphur was found near the earth’s surface, butAmerican miners had to learn (7) to extract sulphur from 1200 to 1500 feet undergrounD、There were many years of experiments. Then they finally found the (8) . Several pipes were drilled down to the sulphur deposits. Some of them carried boiling water, causing the sulphur to (9) . Then other pipes carried the mineral up and (10) of the earth in a liquid form.
Most people do not realize that the manufacture of many common articles (11) on sulphur. Some farmers use compounds of this mineral to (12) insects and plant pests. It is an important ingredient in the manufacture of paper pulp, (13) is used for our books and magazines. Researchers have found that some forms of sulphur can be used in fighting infections. Therefore many (14) include this mineral. Gunpowder, camera and X-ray film, and mbber tires also (15) sulphur.
About eighty percent of all the sulphur (16) goes into the manufacture of sulphurie aciD、In its pure form it has no (17) . However, sulphide compounds (18) have the strong smell of rotten eggs.Although most sulphurie acid is used to make fertilizers and to refine petroleum, it is an ingredient in hundreds of other commodities (19) , from textiles to glue, food preservatives, paint, and (20) glass.
A、how B、what
C、why D、when