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The sum of two positive integers, a and b, is at least 30. The difference of the two integers is at least 10. If b is the greater integer, which system of inequalities could represent the values of a and b?

Aa + b ≥ 30 b ≥ a + 10

B.a + b ≥ 30 b ≤ a – 10

Ca + b ≤ 30 b ≥ a + 10
Da + b ≤ 30 b ≤ a – 10