设个体域D是正整数集
，则下列公式中真值为真的公式是( ).
A:
B:
C:
D:
，则下列公式中真值为真的公式是( ).A:
B:
C:
D:
举一反三
- 某人举步上楼梯，每步跨1个台阶或2个台阶，设上n个台阶的不同方式数为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/62999550ec1547439283cd9872427fdc.png" />，则( ). A: 初始条件为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/e5083263b09044c1b6e95baed3ef628c.png" />=1，<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/07aa95ceccda433f8e9432a186fae005.png" />= 2, 递归关系为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/ad0a958e510040be8f4253d0526d7ce5.png" />(n≥3). B: 初始条件为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/d5cc33a9d0714d3fbba386ccff5f8aaa.png" />=1，<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/34a42e4a62ea448db919ffa607f5de44.png" />= 1, 递归关系为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/c3dc9b741afa4ae68983bc1d5db5e065.png" />(n≥3). C: 初始条件为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/405917811f9845e1915af00c9fa30c79.png" />=1，<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/ccd3e7a79651413b8cd22dbf5cd05ac8.png" />=1, 递归关系为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/0acc9967cdab4f31a918b5fc8fe38608.png" />(n≥3). D: 初始条件为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/245baeee86b943e4bd7f1c39803b142c.png" />=1，<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/a06359868bb1457e81ab7e102d212630.png" />= 2, 递归关系为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/0aee376a7bfa44da9f431ecb21e6c787.png" />(n≥3).
- 下列选项哪些是立体干燥花（ ）。 A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/e0a75b2333b848a4b2deab3fd3cadfaa.png"> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/d11fc544a6f94867affb44c7c8facf5a.png"> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/66be30e1dc6b4777b36729ae181aefeb.png"> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/0b0d4724e987493fb7eb224f50bf0ddf.png">
- 设 A(x):x 是鸟, B(x):x 会飞，命题“有的鸟不会飞”符号化为( ). A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/6fdacd6a161c4b25847f4cd5a68cac5c.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/bb2efef1471b4434a3cb4b0870aef87a.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/37783eb9873b470b948695eade3b0dc4.png" /> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/a59cb9338b1b445d94a7159d2cfa01da.png" />
- 设Zm= {0, 1, 2, …, m - 1}，<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/211f8e3b46b646598e53d85def442786.png" />是模m乘法运算，则(Zm, <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/202010/60da1bba21044182aebb1e783993e81f.png" />)是群.
- 如图所示电路的逻辑表达式F=（ ）。<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/8655693a417e4e43a32e0732ed533c96.png" /> A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/beda73211aea49f082d9137fd4eb0526.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/7388c99ee0824f20bcf85893934a2f6a.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/9a5c81e78b344c79a9389e932a7f55ce.png" /> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/82193a9a030243728012b02e15718987.png" />