在心脏中，自律性最强的结构是（）
A．房室结
B．窦房结
C．房室束
D．蒲肯野氏纤维
参考答案：B
We don’t believe the reason _________ he gave for his being absent from school.
A．that
B．why
C．because
D．for which
在测量跳远成绩时，从落地点拉向起跳线的皮尺，应当与起跳线（ ）．
