使用强心苷引起心脏中毒最早期的症状是
A．房性早搏
B．心房扑动
C．室上性阵发性心动过速
D．室性早搏
E．三联率
参考答案：D
__________along the quiet road at forty miles an hour，and then an old man suddenly started to cross the road in front of me.
A．Driving
B．I was driving
C．Having driven
D．When I was driving
固定密封的O形密封圈的压缩率不得超过（）。
A．15％
B．20％
C．30％
