Can anyone give me a detailed resolution for this exercise?Consider the following Subspace on R3:

U={(x1,x2,x3) € R3: x1-2x2+x3=0}

Which of the following group of vectors is an orthogonal basis of U?

A - {(1,-2,1), (-1,0,1)}

B - {(-1,0,1), (1,1,1)}

C - {(2,1,0), (-1,0,1)}

D - {(2,1,0), (0,0,1)}

E - {(1,-2,1), (-1,0,1), (1,1,1)}