有4个顶点，如何连接4个顶点所用的管道最短？( )。 A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/14e274d424f2476989fefc7ac0a1b877.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/b945aa40fe36479a91b263c96244260d.png" /> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/0323cba80b54453bbb587009da3dbdb7.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/5b0e221bf38e4e15b14c31f5232371d5.png" />

下列选项中所显示的物流动线，那种是L型动线( )。 A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/7e0f82a0f5504475b69ecc599018ad99.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/efb8c10b0c73445ca0b22b8b63e42642.png" /> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/a25290ca26e84832844a5b6f9066c801.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/6234d298d6f947ec96ebee5959b057a5.png" />

在点电荷+q的电场中，若取图中P点处为电势零点，则M点的电势为（）<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/30afa68a13fc4a00808d9f711f0afc52.png" > A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/8c002b151fcb46fdb74074846959a12f.png" >． B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/50bfc21fb91b4d6eb828804d1779cbf5.png" >． C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/8fd7fdf3c864449bb48848c55ba84317.png" >． D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/917054805d0b4b5c83811f863e49a225.png" >．

正弦量<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/68b98b53108b4a51b29f59187058b7a0.png" /> ，则其有效值为（ ）V。 A: 200 B: 100 C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/d95db06d7d764c4a994bf3d58764f20e.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/fd77773fbd7343ec9ed61fac95727df5.png" />

关于质数，下列说法正确的是（ ） A: 存在一个多项式<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/0b3f9359571648eaa323d22b0758008c.png" />，使得对任意自然数<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/5ada649fd5dc4a82b44d0c7d6f8df975.png" />，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/0b3f9359571648eaa323d22b0758008c.png" />都是质数。 B: 若<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/b3ea58bef52b482ba98d9c7b71396c30.png" />是大于1的整数，则在<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/b3ea58bef52b482ba98d9c7b71396c30.png" />的所有正因数中，除1以外的最小正因数<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202010/3c8e01b188544b5bb936484e877bc378.png" />一定是质数。 C: 质数有无数多个。 D: 质数都是奇数。