【单选题】【消耗次数：1】
地球绕日进行公转，当太阳光线垂直照射到南半球回归线上时，是北半球的（）。
①
夏至日
②
冬至日
③
春分日
④
秋分日
参考答案：
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【单选题】
阳光中的紫外线照射到皮肤上可生成( )。
①
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②
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③
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随机题目
【简答题】
8086/8088CPU的数据线和地址线是以[填空1]方式轮流使用的
【简答题】
8086的16位标志寄存器FLAGS中IF=1表示CPU[填空1]中断，TF=1表示CPU进入[填空2]工作方式。
【简答题】
芯片8237A有四个独立的DMA通道，这四个通道在请求DMA传送时的优先权可通过编程设定为[填空1]和[填空2]。
【单选题】
下面关于8251的描述，正确的是（）。
①
8251是一种可编程并行接口芯片
②
8251不能以异步方式发送数据
③
8251不能以同步方式发送数据
④
8251可以以异步方式发送数据，也可以以同步方式发送数据