問題詳情

A great deal of intensive work must be performed in a commercial apple orchard. Each year the trees shouldbe pruned and fertilized, with nitrogen 15 , to grow well and bear properly. Other elements such as potassiumand magnesium are also needed.Frost, insect pests, and fungus diseases are among the most serious problems apple growers face. Open appleblossoms are killed when the temperature drops a few degrees below freezing, and 16 are often lost becauseof spring frosts. Commercial orchards generally are planted on slopes or high ground to reduce this danger, sincecold air tends to sink. Some apple growers protect their orchards with heaters 17 frost occurs in blossomtime.Many insects attack the apple tree. One of the worst is the codling moth, which lays its eggs on or near thefruit. When the eggs hatch, the larvae bore into the fruit and a “wormy” apple 18 . Diseases caused by fungiand bacteria can also infect the flowers, fruit, and leaves of the apple tree.Repeated spraying is often necessary to keep the fruit 19 insects and diseases. Because pests appear atdifferent times of the growing season, some areas may need 12 to 14 sprays per year. New varieties of apples arenow being bred that are resistant to certain kinds of insects and fungi. This reduces the need to spray so often.
15
(A) in place
(B) in particular
(C) at large
(D) at most

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