A、They keep plant from getting warmth. B、They are very cold and can freeze the plants. C、They keep plant tissues from getting wa

Florida is located in the southeastern United States. It’s called the Sunshine State. It grows more oranges than anyplace except Brazil. Recently, Arctic air has damaged some Florida oranges and strawberries, and killed fish at tropical fish farms. However,(16)protecting plants and trees in the garden may not be too difficult if you follow a few suggestions. Sudden cold can be the biggest threat, especially after a warm period. Plants have not had a chance to harden their defenses. Those that are actively growing or flowering are at high risk. Try to choose planting areas that face west and south. (17)Being near other growth may also provide warmth. Most frost damage takes place at night. Ice crystals form on the leaf surface.(18)They pull moisture from the leaves and keep plant tissues from getting water. Cold weather is most likely to damage or kill plants that do not have enough moisture. So keep the garden watered. Moist soil absorbs more heat than loose, dry soil covered with vegetation. University of Arizona extension experts say covering plants and small trees with cloth or paper can help prevent frost damage. A 100-watt light bulb designed for outdoor use can also provide warmth. Some people place Christmas lights on young trees for warmth. The bulbs should hang below the leaves to let the heat rise into the tree.
16. What’s the main idea of the passage?
17. Which one is an improper way to protect trees?
18. How do ice crystals damage the plants?