Final answer:
The trigger for using the present subjunctive in Spanish that is associated with expressing doubt, disbelief, or denial is 'No creo que...'. This phrase sets up a situation where the outcome is uncertain, which is when the subjunctive mood is appropriately applied in Spanish.
Step-by-step explanation:
The trigger associated with the use of the present subjunctive expressing doubt, disbelief, or denial is "No creo que..." This expression is used when someone wants to convey that they don't believe something is true, indicating a sense of uncertainty or doubt, which requires the subjunctive mood.
The subjunctive mood in Spanish is commonly used to express wishes, suggestions, or scenarios that are hypothetical or not certain to occur, which includes expressions of doubt like 'No creo que.'