In the abstract module there is a possibility to create keywords for a pulldown menu, so the author has to choose from the list you create.
Please follow the next steps to create the keywords.
Go to the Module settings of the conference and check the box at 'Advanced Keyword Field Configuration'.
Go to the Module content -> Keywords -> Add keyword to add 1 keyword or Import to import an excel file.
Go to Page editor -> Abstract wizard -> abstract data -> click with the right mouse button on the keyword field -> field properties -> choose the Pulldown field radio button
Repeat step 3 to choose the pulldown menu for the other keywords.
How the author sees it: