# 单元测试三 <quiz> <question> <p>1.[单选](2分)启动ROS Master的命令是：</p> <answer correct>A.roscore</answer> <answer>B.rosmaster</answer> <answer>C.rosMaster</answer> <answer>D.roslaunch</answer> <explanation>你选对了</explanation> </question> </quiz> <quiz> <question> <p>2.[单选](2分)关于ROS Node的描述，哪一项是错误的?</p> <answer>A.Node启时会向Ｍaster注册</answer> <answer correct>B.Node可以先于ROS Master启动</answer> <answer>C.Node是ROS可执行文件运行的实例</answer> <answer>D.Node是ROS的进程</answer> <explanation>你选对了</explanation> </question> </quiz> <quiz> <question> <p>3.[单选](2分)关于.launch文件的描述，以下哪一项是错的?</p> <answer>A.可以加载配置好的参数，方便快捷</answer> <answer>B.通过roslaunch命令来启动launch文件</answer> <answer correct>C.在roslaunch前必须先roscore</answer> <answer>D.可以一次性启动多个节点，减少操作</answer> <explanation>你选对了</explanation> </question> </quiz> <quiz> <question> <p>4.[单选](2分)想要查看`/odom`话题发布的内容，应该用哪个命令?</p> <answer correct>A.rostopic echo /odom</answer> <answer>B.rostopic content /odom</answer> <answer>C.rostopic info /odom</answer> <answer>D.rostopic print /odom</answer> <explanation>你选对了</explanation> </question> </quiz> <quiz> <question> <p>5.[单选](2分)请练习rosmsg命令，下列哪个不是std_msgs下的消息?</p> <answer correct>A.std_msgs/LaserScan</answer> <answer>B.std_msgs/Header</answer> <answer>C.std_msgs/Time</answer> <answer>D.std_msgs/Float32</answer> <explanation>你选对了,LaserScan在sensor_msgs功能包下</explanation> </question> </quiz> <quiz> <question multiple> <p>6.[多选](5分)关于Topic通信的描述，正确的选项有：</p> <answer correct>A.Topic是一种异步通信机制</answer> <answer>B.一个Topic至少要有一个发布者和一个接收者</answer> <answer correct>C.查看当前活跃的Topic可以通过rostopic list命令</answer> <answer>D.一个Node最多只能发布一个Topic</answer> <explanation> B、错误。一个Topic可以被发布而无人接收，也可以一直被接收而无人发布。 D、错误。一个Node可以发布多个Topic，例如仿真示例中的/gazebo节点。</explanation> </question> </quiz> <quiz> <question> <p>7.[判断](2分)同一个Topic上可以有多个发布者.</p> <answer correct>A.正确</answer> <answer>B.错误</answer> <explanation>一个Topic上可以有多个发布者，例如/tf, /rosout</explanation> </question> </quiz>