A. THEM B. US C. IT D. ONE PART 2. READ THE PASSAGE AND C...

14. A. them B. us C. it D. one Part 2. Read the passage and choose the best answer. Fertilizer is any substance that can be added to the soil to provide chemical elements essential for plant nutrition so that the yield can be increased. Natural substances such as animal droppings, ashes from wood fires, and straw have been used as fertilizers in fields for thousands of years, and lime has been used since the Romans introduced it during the Empire. It was not until the nineteenth century, however, that chemical fertilizers became widely accepted as normal agricultural practice. Today, both natural and synthetic fertilizers are available in a variety of forms. A complete fertilizer is usually marked with a formula consisting of three numbers, such as 4-8-2 or 6-6-4, which designate the percentage of content of nitrogen, phosphoric acid, and potash in the order stated. Synthetic fertilizers, produced by factories, are available in either solid or liquid form. Solids, in the shape of chemical granules, are in demand because they are not only easy to store but also easy to apply. Recently, liquids have shown an increase in popularity, accounting for about 20 percent of the nitrogen fertilizers used throughout the world. Formerly, powders were also used, but they were found to be less convenient than either solids or liquids. Fertilizers have no harmful effects on the soil, the crop, or the consumers as long as they are used according to recommendations based on the results of local research. Occasionally, however, farmers may use more fertilizer than necessary, in which case the plants do not need, and therefore do not absorb, the total amount of fertilizer applied to the soil. The surplus of fertilizer thus can damage not only the crop but also the animals or human beings that eat the crop. Furthermore, fertilizer that is not used in the production of a healthy plant is leached into the water table. Accumulation of chemical fertilizer in the water supply accelerate the growth of algae and, consequently, may disturb the natural cycle of life, contributing to the death of fish. Too much fertilizer on grass can cause digestive disorders in cattle and in infants who drink cow’s milk. Fertilizer must be used with great attention to responsible use or it can harm the environment.