‍一弹簧振子作简谐运动，当位移为振幅的一半时，其动能为总能量的‍ 未知类型：{'options': ['[img src="http://img0.ph.126.net/jpAueoBytuZa6k2wwwW9OA==/855683929300814862.jpg"]', '[img src="http://img0.ph.126.net/wUiBfDcpwubnnTfUqXWe8g==/2988138352860486966.jpg"]', '[img src="http://img0.ph.126.net/BmhE5DieqvLPa8Q2yuK6PQ==/2077566803201671014.jpg"]', '[img src="http://img0.ph.126.net/OaayZdr_Aj3S8aprU5kpSA==/6619163353304620563.jpg"]'], 'type': 102}

电磁场量的法向边界条件为（）。 未知类型：{'options': ['[img src="http://img0.ph.126.net/EsIkaXjnKukiyimHp6dYpQ==/6630400362140980911.png"]', '[img src="http://img1.ph.126.net/Qvas15HCDc_RrWbLruYPRw==/6619063297747523047.png"]', '[img src="http://img0.ph.126.net/DRI9k3pVjDPeDmngiOgT3Q==/6630279415861923459.png"]', '[img src="http://img2.ph.126.net/IiW1SDf3LX-s_IKSk4Vpvg==/6619471216561427789.png"]'], 'type': 102}

设总体X～N(μ,σ^2),μ和σ是未知参数。为估计参数σ^2的置信区间，应选T=____________作为枢轴变量,并且T服从______。? <img src="http://img2.ph.126.net/SHUrsWncVzw3TbqMT630Ug==/6632510324955921443.png" /><br />|<img src="http://img2.ph.126.net/I5VmIURcDfhDZIPIQy5JZw==/6632334403095483329.png" />|<img src="http://img0.ph.126.net/v1kDLV9rE4i9IWRPugufXQ==/6632404771839652521.png" />|<img src="http://img0.ph.126.net/sQOy3VhGtuk-bcM7dsC3kQ==/6632272830444326010.png" />

n位触发器构成的扭环形计数器，其无效状态数有( )个。? <img src="http://img1.ph.126.net/syawN86lkJeyXf8emf2enw==/6630087001327300267.png" />|<img src="http://img2.ph.126.net/0JBcfdqdyUjt5-uTh7cmUQ==/4886405595797893661.png" />|<img src="http://img2.ph.126.net/qBQGx0Z9T_pt4PZJc8Nn7g==/6608560762678510607.png" />|<img src="http://img0.ph.126.net/elyGxaiPbD815O67sULOnQ==/1876312194853825038.png" />

下列化合物有旋光性的是( )。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201907/42754375451947b4a2097a204914e285.png" border="0" vspace="0" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201907/259cc0f9369441888e4306c19039152f.png" border="0" vspace="0" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201907/c6798f5eb7e14df7a79f40cdd7d2f42e.png" border="0" vspace="0" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201907/4275928f484d4bad94705297fe159cf0.png" border="0" vspace="0" />