In ABC, AB=c cm, AC= b cm and CB=a cm, If A=2 B, then which of the following is true?

• A. $$ {a^{2}=b^{2}-bc}$$
• B. $$ {a^{2}=b^{2}-ac}$$
• C. $$ {a^{2}=b^{2}+bc}$$
• D. $$ {a^{2}=b^{2}+ac}$$