You can use the Audio option to record audio for your students to listen to within a formative. This is helpful for assessing listening skills, multi-sensory learning (having a reading passage read-aloud), accommodations (having questions read-aloud) and more!
Click on the "+" icon
Choose "Audio" from the red icons
Click "Record Audio":
Note: Each recording has a 10 minute limit, so you should have plenty of time to read questions, instructions, and passages, but plan ahead to make multiple recordings if needed.