The economy of a small town in Europe depended on agriculture in 1920. With the development of industries in 1940, the economy relied more on industries. Due to the release of lot of soot by these industries, the bark of the trees became permanently dark within ten years. The primary source of food for birds was a certain species of moth which spent most of their time sitting on tree trunks and laying eggs in the bark of the tree.
Year
White moths (%)
Black moths (%)
1920
95
55
1930
95
5
1940
95
5
1950
50
50
1960
20
80
1970
5
95

The shift in the moth percentage can be best explained by one of the statements.

The white moths no longer blended with the color of the tree bark and, thus, were selected for.

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The black moths blended better with the color of the tree bark and, thus, were selected for.

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The black moths blended better with the color of the tree bark and, thus, were selected against.

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The white moths blended better with the color of the tree bark and, thus, were selected against.

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The black moths did not blend with the color of the tree bark and, thus, were selected against.

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Solution

The correct option is A The black moths blended better with the color of the tree bark and, thus, were selected for.
Option B is the correct answer as the black moths blended better with the color of the tree bark and, thus, were selected for.
Because the percentage of black moths is increasing, they must be selected for. This eliminates C and E. Because the percentage of white moths is decreasing, they must be selected against, eliminating choice A. Choice D is wrong because white moths would not blend better against dark tree bark.

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The economy of a small town in Europe depended on agriculture in 1920. With the development of industries in 1940, the economy relied more on industries. Due to the release of lot of soot by these industries, the bark of the trees became permanently dark within ten years. The primary source of food for birds was a certain species of moth which spent most of their time sitting on tree trunks and laying eggs in the bark of the tree.

Year	White moths (%)	Black moths (%)
1920	95	5
1940	95	5
1950	95	5
1960	50	50
1970	20	80
1980	5	95

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Q. Read the following passage and answer the following question.
In 1910, a small town on the East Coast of the United States relied primarily on agriculture to support its economy. In the mid-1930s, a steel mill was built, and the economy shifted from being agriculturally supported to being industrially supported. The steel mill released a lot of smog and soot into the air, which collected on the bark of trees in a wooded area near the outskirts of town. Over a period of ten years the bark gradually darkened, then maintained a constant dark color. A variety of animals and insects lived in the wooded area. In particular, a certain species of moth served as the primary food source for a population of birds. The moths lay their eggs in the bark of the trees and, thus, must spend a fair amount of time sitting on the tree trunks. Table 1 presents data on the moth population.Table 1

Year	White moths (%)	Black moths (%)
1910	95	5
1920	95	5
1930	95	5
1940	50	50
1950	20	80
1960	5	95

Birds track their prey visually, whereas bats rely on sonar to locate to locate their food. If the bird population were replaced with a bat population in 1940, what would be the ratio of white moths to black moths?

Read the following passage and answer the following question.
In 1910, a small town on the East Coast of the United States relied primarily on agriculture to support its economy. In the mid-1930s, a steel mill was built, and the economy shifted from being agriculturally supported to being industrially supported. The steel mill released a lot of smog and soot into the air, which collected on the bark of trees in a wooded area near the outskirts of town. Over a period of ten years the bark gradually darkened, then maintained a constant dark color. A variety of animals and insects lived in the wooded area. In particular, a certain species of moth served as the primary food source for a population of birds. The moths lay their eggs in the bark of the trees and, thus, must spend a fair amount of time sitting on the tree trunks. Table 1 presents data on the moth population.

Table	% white moths	% black moths
1910	95	5
1920	95	5
1930	95	5
1940	50	50
1950	20	80
1960	5	95

If a seed from one of the trees was planted in an area far from the steel mill, what color would the bark of the tree be?

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