SQL Quiz: Using a covering index

Task 182:

The actor table has an index idx_actor_last_name on the last_name column. Which of the following queries can use this index as covering index?

select last_name from actor order by last_update;

select distinct last_name from actor;

select last_name, count(*) from actor group by last_name;

select last_name, last_update from actor order by last_name desc;

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