【名词&注释】
工作面(face)、体外受精(in vitro fertilization)、感觉神经(sensory nerve)、同源人工授精(artificial insemination by husband)、下颌前磨牙(mandibular premolar)、异源人工授精(artificial insemination by donor)、无性生殖(asexual reproduction)、龈下牙石(subgingival calculus)
[单选题]用匙形刮治器刮除龈下牙石(subgingival calculus)时,工作面与牙面之间的角度应为
A. 120°
B. 110°
C. 90°
D. 80°
E. 30°