Which operation shows that polynomials are a closed system under addition?

Question

Responses

(2x2+6x+1)+(3x2+3x+9)=(2x2+3x+1)+(3x2+6x+9)

(2x2+6x+1)+(3x2+3x+9)=5x2+9x+10

(2x2+6x+1)+(3x2+3x+9)=(2x2+3x2)+(6x+3x)+(1+9)

(2x2+6x+1)+(3x2+3x+9)=−x2+3x−8

Answer 1

The correct response is: (2x^2+6x+1)+(3x^2+3x+9)=(2x^2+3x^2)+(6x+3x)+(1+9)