孕（ ）周需做B超查胎儿颈后透明层（NT）。http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/1aff763f890b446abd55caea6d269916.png
举一反三
- 孕（）周需做B超查胎儿颈后透明层（NT）。http://image.zhihui...bd55caea6d269916.png
- <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/2205d9f03e724a04b34f2f1045309079.png" />的幅频响应是，幅频响应是。 A: 1，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/760d7fcc2f264ed1b10fb836cb48f565.png" /> B: -1，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/21f685d2962e4b6993bfcaa513bdbf68.png" /> C: 2，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/57267e995f86426899ce3cc0177a2343.png" /> D: 1，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/ea8ba62853a94a15a5620c5165e3594a.png" />
- LTI离散系统的差分方程为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/eb2e05fecafa414e98c3ffaf0b435e82.png" />，当激励<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/f6bdc410c9fd42b8b8dd675197919ceb.png" />时，求零状态响应<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/12bfebbed6b14e298e09c4cb1940677b.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/69fc6db7834143a292ce24d4829a06e6.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/f7af4326d64c44669cd0f0d4c7b23eb1.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/f929cab698bd4309a4649201e7f5604c.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/81108c43b5f2457291e3723cc96280e1.png" />
- 已知系统的差分方程为：<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/4d2011df82b5487b90c89c82392b7635.png" />初始状态<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/69fdc69872fc4526b3406d4e545b5423.png" />输入信号为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/75e7d55edcb246e396b63e810f4b0c5f.png" />求系统的零输入响应。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/f3d4c0dc2e044821ad7f2fa06ae922de.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/5b82c0acece14a83ad58bc9d533a1885.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/06178caff4d54505b3a9dbfcd3f413ea.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/0b7c106121734430927a095f909fe51f.png" />
- 设<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/caa2009d65b9414e9eee2f311038ed51.png"/> 为系统输入，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/af57e24c7bb247e29a81996211b39e9d.png"/>为系统输出，则下列关系式中为线性时不变系统的是（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/6d8d3ed4bbb5472d8ad95cf86ff40033.png"/> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/553b7fd10b744a38859127a91414813b.png"/> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/e59a6933e2c647d4b5c12b2ebb0a0ff6.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/4835c010dc244facb01784095e9bd080.png"/>