A simple way to add a background under a text object using only one object:

• Add a text Object in Objects and Animation (O&A)
• Click on Drop Shadow in the Common Tab of O&A
• Click on Customize in the Common Tab of O&A
• In the Drop Shadow and Glow box click on Spread
• In the dropdown menu click on “Cove - Deep” or “Cove - Shallow”
• Adjust the “Distance and Size”
• Click in the “Color” box and choose a background color
• Adjust the Opacity

This approach can be used for text comments to automatically add background to all text comments on all slides.