Which of the following blade angle is appropriate for scaling and root planing

Blade angulation. (A) 0 degrees: correct angulation for blade insertion. (B) 45 to 90 degrees: correct angulation for scaling and root planing. (C) less than 45 degrees: incorrect angulation for scaling and root planing. (d) More than 90 degrees: incorrect angulation for scaling and root planing, but correct angulation for gingival curettage.