Remove duplicate rows
80%
Remove Duplicates keeps the first copy of each row and deletes the rest. Unlike filtering, this one really does delete, so the habit worth building is to copy the list somewhere first, or at least to know that Ctrl+Z works.
It compares whole rows across whatever range you give it. Two rows that differ only in a trailing space count as different, which is the TRIM lesson arriving again from another direction.
This list has two addresses repeated. Use the Remove duplicates panel on the email column to take them out.
A2
Click a cell and type. Enter commits, Tab moves right, F2 edits in place, Ctrl+Z undoes. Drag the small square at the corner of a cell to fill. Ctrl+Enter checks your answer.
This one really deletes. Ctrl+Z puts it back.