Choice D is correct. Since each choice has a term of \(3 x ^2\), which can be written as \((3 x)(x)\), and each choice has a term of \(14 b\), which can be written as \((7)(2 b)\), the expression that has a factor of \(x + 2 b\), where \(b\) is a positive integer constant, can be represented as \((3 x + 7)(x + 2 b)\). Using the distributive property of multiplication, this expression is equivalent to \(3 x(x + 2 b)+ 7(x + 2 b)\), or \(3 x ^2 + 6 x b + 7 x + 14 b\). Combining the x-terms in this expression yields \(3 x ^2 +(7 + 6 b)x + 14 b\). It follows that the coefficient of the x-term is equal to \(7 + 6 b\). Thus, from the given choices, \(7 + 6 b\) must be equal to \(7\), \(28\), \(42\), or \(49\). Therefore, \(6 b\) must be equal to \(0\), \(21\), \(35\), or \(42\), respectively, and \(b\) must be equal to \( /6\), \(21/6\), \(35/6\), or \(42/6\), respectively. Of these four values of \(b\), only \(42/6\), or \(7\), is a positive integer. It follows that \(7 + 6 b\) must be equal to \(49\) because this is the only choice for which the value of \(b\) is a positive integer constant. Therefore, the expression that has a factor of \(x + 2 b\) is \(3 x ^2 + 49 x + 14 b\). Choice A is incorrect. If this expression has a factor of \(x + 2 b\), then the value of \(b\) is \(0\), which isn't positive. Choice B is incorrect. If this expression has a factor of \(x + 2 b\), then the value of \(b\) is \(21/6\), which isn't an integer. Choice C is incorrect. If this expression has a factor of \(x + 2 b\), then the value of \(b\) is \(35/6\), which isn't an integer.