题干
He didn't selfishly keep for himself the money inherited from his uncle. Instead, he made a ______ contribution to help the community.
A：commercial
B：generous
C：comparable
D：profitable
答案(点此获取答案解析）
B
仪，A为汽车，两者相距335 m，某时刻B发出超声波，同时A由静止开始做匀加速直线运动．当B接收到反射回来的超声波信号时，A、B相距355 m，已知声速为340 m/s，则汽车的加速度大小为：
