题目如图,由999个完全相同的小正方形拼接而成的3×33\times 33×3网格,图形ABCDABCDABCD中各个顶点均为格点,设∠ABC=α\angle ABC=\alpha∠ABC=α,∠BCD=β\angle BCD=\beta∠BCD=β,∠BAD=γ\angle BAD=\gamma∠BAD=γ,则α−β−γ\alpha -\beta -\gammaα−β−γ的值为( )A.30∘30^{\circ}30∘B.45∘45^{\circ}45∘C.60∘60^{\circ}60∘D.75∘75^{\circ}75∘知识点:余角和补角章节:图形的性质 / 图形认识初步