滚动轴承上没有注出级别代号，说明此轴承的级别为（）。
A.C级
B.D级
C.E级
D.G
参考答案：D
He sat at the front ________ be able to hear everything the teacher said.[ ]
A．so as to
B．due to
C．thanks to
D．owing to
锅炉房内必须备有防火砂箱（袋）或化学灭火剂。
