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