应该是胶合面为B级别的胶合板.
因为在北美胶合板一般分A,B,C和D四个级别.
参照：
The common veneer grades for plywood are A,B,C,C-plugged and D.The plywood panel itself is defined by the grade of the face and back veneers (e.g.,A-B or C-D).