台秤空载时计量杠杆不起摆是（）以外的原因所致。

A.被称量的物体少

B.平衡调整铊未调整

C.计量杠杆刀系配置不当

D.系统阻滞过大，视准器有粘物或磁性

I’m fine — I just felt a bit sleepy and tired, that was ________ I went to bed so early."

A．because

B．when

C．that

D．why