单选题
Anyone planning to go camping or hiking should first learn to recognize poison ivy, (1) this plant can cause a rash resulting in reddened skin, an annoying itch, and painful blisters. A severe (2) can even force a person to remain in bed or become hospitalized. The best way to (3) these discomforts is to avoid the plant. Fortunately this plant is easy to (4) Whether it grows as a bush or a vine, the shape of its leaves is always (5) . Each leaf stalk has three glossy leaves, usually with jagged edges. In early spring the leaves are red, (6) to green later on. Then in the fall, they (7) to bright red or orange. The poison ivy plant is found (8) everywhere in North America. Because many birds eat its berries, its seeds are (9) distributed. The plant loves the sun and flourishes along beaches, in fields, and by roadsides. It also grows (10) in light shade and is often found in parks and pine forests. However, in thick woods the story is (11) . It is not (12) there. That is because the leaves of the trees block out the sun, (13) the plant needs to grow. The poison in poison ivy is in the form of an oil that is in all parts of the plant. It is extremely (14) . Merely touching the plant is enough contact for a person to be infected by the (15) . Touching clothing or shoes that have brushed against the plant can also cause a rash and blisters. Even the smoke from a fire (16) poison ivy is burning can cause the skin poisoning. A person who makes (17) with the plant should wash all infected areas with a strong laundry soap as soon as possible. Clothes that have come in contact with the (18) should be dry cleaned or washed in soap and water. There is one good way to prevent the (19) : (20) away from the plant!