turtlebot3 not moving in simulation mode. [closed]

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Hi guys, I have tested that the robot can move in a real environment. Tring to move the robot in simulations but not working. First, run the virtual world command

roslaunch turtlebot3_gazebo turtlebot3_world.launch

then run the tele control command

roslaunch turtlebot3_teleop turtlebot3_teleop_key.launch

The virtual robot doesn't respond to the tele control.

And I run rqt_graph, there a three node "/gazebo" "/gazebo_gui" "/turtlebot3_teleop_keyboard". And I check the topic "/cmd_vel", no one was subscribing it.

Isn't any connections between these topics. Did I miss any command?