Using a covering index

Question

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?

Answer 1

select last_name from actor order by last_update;

Answer 2

select last_name, last_update from actor order by last_name desc;

Answer 3

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

Answer 4

select distinct last_name from actor;