图示结构中B结点的不平衡力矩（约束力矩）为：（）<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/88c7b2d7d28442138ce55089cf7b9336.png"> A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/47d0574ad121412e9d4157cfefdbe4e2.png"> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/44cf62aafb4448249c125acf30fafc34.png"> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/c03f18530c2449adb6c23d46c25bcb46.png"> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/a75bc93c9f754579b24d7dc9c1705930.png">

下列关于极值命题中正确的是（） A: 若<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/66e36e20da3f43e9bbd9ce0f42dcbe28.png">，则<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/9d60dd3351b54052b4f4afe27423a0e7.png">必是<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/53f1ecb5821b44f1a56bbc836e49d9b7.png">的极值点 B: 若<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/0a40a2ad34e649e3b999f776e8fe1919.png">，则<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/9d60dd3351b54052b4f4afe27423a0e7.png">必是<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/53f1ecb5821b44f1a56bbc836e49d9b7.png">的极值点 C: 极大值一定大于极小值 D: 若<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/31b1a07ab57347febde3751859364dfb.png">存在且<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/9d60dd3351b54052b4f4afe27423a0e7.png">是极值点，则必有<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/66e36e20da3f43e9bbd9ce0f42dcbe28.png">

计算机控制系统中，若被控对象传递函数为<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/449150d9457a43b98c14899c6ffa5b27.png" >，设采样周期T=1s，则其广义被控对象的脉冲传递函数为（）。 A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/eda76ecd0c754547a9d40ec652dd6389.png" > B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/950619299fc9457cab633a4abf11df94.png" > C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/f1b3a243951e47f0965e825c0ef3d0d8.png" > D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202007/817b81563181439e8e54ea1de38e039f.png" >

设随机变量[img=136x83]17d60b79c1d7ac5.png[/img]独立同分布，记[img=616x84]17d60b79d977831.png[/img]，则随机变量[img=52x84]17d60b79ec0e1bf.png[/img]与[img=52x68]17d60b79fe65ba3.png[/img]之间的关系必然是（）。 A: 不独立 B: 相关系数等于0 C: 独立 D: 相关系数不为0

设随机变量X~N(4,2)，则其特征函数为(). A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/357ad388efa144a1a2b824e2b1ded239.png" > B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/d52e72841a81484981168cbb693bad24.png" > C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/00e1e0c2bba04889b58eb483c88821fb.png" > D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/1851c30670244a5c821128d6c44a3ecc.png" >