LG 98TR3PJ-B Owner's Manual page 147

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[Selector]
Click the button on the button panel to access the selector part. You can select one or some students to answer
your question randomly.
Only if at least 1 student in your class, you can start the selector.
[Start]
Click the "+" button or "-" button to set number of person(s) whom will be selected. Click [Start] to start selecting or
click to quit.
[Reset]
Click [Reset] to restart the selector.