A couple decides to have 4 children. If they succeed in having 4 children and each child is equally likely to be a boy or a girl, what is the probability that they will have exactly 2 girls and 2 boys?
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A\frac{3}{8}
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B\frac{1}{4}
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C\frac{3}{16}
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D\frac{1}{8}
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E\frac{1}{16}