Nobody knew who was the first ________ at school that morning when the window was broken.
A：arriving
B：arrived
C：to arrive
D：have arrived
美国有权对总统提出弹劾的是（ ）
已知：△ABC中，∠C=90°，AC=5cm，AB=13cm，以B为圆心，以12cm长为半径作⊙B，则C点在⊙B____.
地球上昼夜更替的周期约为
