Final answer:
To add the phrase 'Coming soon!' to a wave-shaped object on a slide, click inside the shape and start typing the text directly.
Step-by-step explanation:
To incorporate the text 'Coming soon!' into a wave shape positioned at the top of a slide, you should take the following action: Click inside the shape and type 'Coming soon!'. Therefore, the correct answer is a) Click inside the shape and type Coming soon! Doing so will allow the text to assume the form and contours of the predefined shape, which in this case is presumably designed to resemble a wave.