Đáp án đúng: B
Giải chi tiết:\(\begin{array}{l}\,{\left( {2x + 1} \right)^3} = 125\\\,\,\,\,\,\,\,\,{\left( {2x + 1} \right)^3} = {5^3}\\\,\,\,\,\,\,\,\,\,2x + 1\,\, = \,\,5\\\,\,\,\,\,\,\,\,\,2x\,\,\,\,\,\,\,\,\,\, = 5 - 1\\\,\,\,\,\,\,\,\,\,2x\,\,\,\,\,\,\,\,\,\, = 4\\\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\, = 2.\end{array}\)
Vậy \(x = 2.\)
Chọn B.