Which one would be better to use in the following sentence? How can I know in the future which of these I should use?

The study deals with the principles of a probabilistic decision support system which-that handles the problem of warning before users are trapped with the attackers’ first move.

  • It's a free choice here between a that relative and a wh one. This is the case with virtually all integrated (defining) relatives. I don't think you need concern yourself with the minor exceptions at this stage of your learning. Incidentally, supplementary (non-defining) relatives virtually always take only wh relatives
    – BillJ
    Feb 11 '21 at 9:43

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