For the following queries, determine the minimum cost of the query (in I/Os), if you can have any number of secondary (also known as alternative-2) indexes available. Each index has to be on a single key attribute; composite keys are not allowed. a) select count(*) from employees where name = ‘John Smith’; b) select avg(salary) from employees where name = ‘John Smith’; c) select count(*) from employees where birthdate < ‘1-1-1980 00:00’;