Method 1: Visual judgment: You can refer to the 45-degree angle and know that B is slightly larger than the 45-degree angle and A is slightly smaller than the 45-degree angle or slightly larger than 135 angle. If a is slightly greater than 135, then A+B is greater than 180. So it is finally determined that A is slightly less than 45, and option B is excluded, and then options A and C are approaching.

Method 2: Calculate COSA and SINB according to the formula COS (π-(a+b)) =-COS (a+b) =-(COSA COSB-SINA SINB), and then select D as the result.