Đáp án đúng: B
Giải chi tiết:\(\begin{array}{l}\,\,A\left( x \right) + B\left( x \right) = \left( {{x^5} - 2{x^4} + 5x - 3} \right) + \left( { - {x^5} + 3{x^3} + 5x + 11} \right)\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {x^5} - 2{x^4} + 5x - 3 - {x^5} + 3{x^3} + 5x + 11\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {x^5} - {x^5} - 2{x^4} + 3{x^3} + 5x + 5x - 3 + 11\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = - 2{x^4} + 3{x^3} + 10x + 8\\A\left( x \right) - B\left( x \right) = \left( {{x^5} - 2{x^4} + 5x - 3} \right) - \left( { - {x^5} + 3{x^3} + 5x + 11} \right)\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {x^5} - 2{x^4} + 5x - 3 + {x^5} - 3{x^3} - 5x - 11\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {x^5} + {x^5} - 2{x^4} - 3{x^3} + 5x - 5x - 3 - 11\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 2{x^5} - 2{x^4} - 3{x^3} - 14.\end{array}\)
Chọn B