某些涂料比另一些涂料更能容忍较差的表面状况
参考答案：对
运用旋转矩阵,求直线2x+y-1=0绕原点逆时针旋转45°后所得的直线方程.
Bob would have helped us yesterday, but he _________. [ ]
A. had been busy
B. is busy
C. was busy
D. will be busy
