为使锅垢中难溶于酸的CaSO4转化为易溶于酸的CaCO3，常用Na2CO3处理，反应式为CaSO4+CO32-<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/88320eab77594b6abf0039ab0efe3c57.png" />CaCO3+SO42-，此反应的标准平衡常数为（）。 A: K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaSO4)·K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaCO3) B: K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaCO3)/K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaSO4) C: [K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaSO4)·K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaCO3)]1/2 D: K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaSO4)/K<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8c371ce6b96487e829331bb8dee134f.png" />(CaCO3)

从数字<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/2d61a913ea754ceab9283348404e99b8.png" >中任取两个不同的数字，则这两个数字之差的绝对值的数学期望为()。 A: 1 B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/7da33d3a3bd54a188acf94dfdbab4f56.png" > C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e8d44a97a0d141198c56ce68511897c9.png" > D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/fa3d4d77c7ea4487a9fd484134badc5e.png" >

某最小相位系统的开环对数幅频特性曲线<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/bcd21e42b27341478945568b99d0e0e1.png" >如图所示，则其开环传递函数和相角裕度分别为（）。<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/84e4b98286924479ae7d38d3b0e5fd2f.png" > A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/b0eda84a8f794aaab38a2ca259435434.png" > B: 0° C: 16.3° D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/aa67284249764b51bb1c9fb836c2a9aa.png" >

已知10箱产品中有8箱次品率为0.1，2箱次品率为0.2，现从这批产品中任取一件，则该件产品是次品的概率为（）。 A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/837e9ce6309b444c987c0de8493c5706.png" > B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/acc5ae591cba42eca4c4b7fbbcc590a6.png" > C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/e6ceeed836d84a7aa08fed75b432f4d3.png" > D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/a947488c7cbf4e469e7d1766a3a1f7df.png" >

设样本空间Ω={1，2，10}，事件A={2，3，4}，B={3，4，5}，C={5，6，7}，则事件=()。https://image.zhihuishu.com/zhs/doctrans/docx2html/201911/3ea3b26fd19f4957ab04eb250c653f49.png