(1 point) Which of the following sets are subspaces of R3? A. {(x, y,z) | 3x−2y=0,7x+4z=0} B. {(4x−9y,−6x−8y,5x+8y) | x, y arbitrary numbers } C. {(x, y,z) | x, y,z>0} D. {(x, y,z) | 6x−5y+9z=−4} E. {(x, y,z) | x+y+z=0} F. {(x, x−3,x+2) | x arbitrary number }