Hi Edward,
Andrew is right that JavaScript is the better solution for this interaction. With Storyline alone, you would need a way to remove the focus from the text entry field in order to validate the learner's input and generate an error if words are mistyped. I suggest validating the entire phrase (all three words) before jumping to the Dropdown layer. Instruct the learner to hit ENTER when typing is complete. If the typed words are incorrect, show the Incorrect layer; if all is correct, show the Dropdown layer. This can be achieved with just two triggers. Please see the attached demo for a detailed example.
