如图所示，在平面直角坐标系xOy中，点B，C分别在x轴和y轴非负半轴上，点A在第一象限，且∠BAC=90°，AB=AC=4，那么O，A两点间距离的（　　）

小林在小学学习时一直比较轻松。进入中学后，由于学习任务增多，加上自己有时不认真听课，课后没有及时复习，作业写得很慢，考试成绩也慢慢下降。这则材料告诉我们（  ）

阅读理解
(Mr. Zhang is showing Wei Fang and Li Lei a modern factory.)
Mr. Zhang: You can’t see many workers here, but you can see a lot of robots. Look, that robot has two big hands.
Wei Fang: How strong it looks!
Mr. Zhang: Yes. It does much work for us.
Li Lei: There are so many big boxes here. What are the robots doing?
Mr. Zhang: They are making fridges.
Wei Fang: How fast they are working!
Li Lei: How much time do they need to make a fridge, Mr. Zhang?
Mr. Zhang: About five minutes.
Wei Fang and Li Lei: Only five minutes! What a modern factory it is!