You can annotate (underline) question texts and images in the Student's view of the Assignment.
You can also annotate (underline) student's Free-Response Question responses.

Annotations (Underline) in Student's View

Enter the Monitor Assignment Page by clicking Monitor icon on an Assignment card.
Click a student’s name to navigate within the student's Assignment to begin marking.
Alternatively, click the Question number in the Heatmap to View All Responses. You can also click on a student’s name to navigate to the particular Activity for the entire Class Group, starting with the student you clicked.
Use your cursor to highlight any texts and select the colour. It is also possible to create multiple overlapping underlines.
To leave an Annotation on an image, click Add Note to Image icon and click anywhere on the image.
Key in your Notes in the text box.
You may insert mathematical or chemical equations, include emoticons, a drawing or upload a file or audio recording.
You can include Keyword Tags to improve the search results.
Select the checkbox beside Notify student(s) if you wish to notify you students about the Annotation you have made.
Once you are done, click Save.
Annotation Notes will be visible in the Annotation Drawer. Click the Notepad icon to Expand/Hide the drawer.
Both teachers and students can leave Comments on your Annotations.

Video Tutorial

(A3,1) Add Teacher Comments

(A3,3) Mark Google Attached Files