Exercise 3.5.14

Row space basis can be the nonzero rows of $U$ : $(1,2,3,4),(0,1,2,3),(0,0,1,2)$; nullspace basis $(0,1,-2,1)$ as for $U$; column space basis $(1,0,0),(0,1,0),(0,0,1)$ (happen to have $C(A)=C(U)=R^3$ ); left nullspace has empty basis.