Which of the following is a subspace of R^3? Justify your answer.

Which of the following is a subspace of R3 ? Justify your answer. i) W = {(x,y,z) |3x+2y+z= 0} ii) W: {(Jit,y,z)|1l:2 +y2 +z2 = 9} iii) W: {05052) Ix = y+1} iv). W = {(3x,2x,5x) |x is a real number}