查询月固定费用是5.9元，8.5元，10.5元或者没有月固定费,下列sql语句正确的是：( )
select id,base_duration,base_cost,unit_cost from cost where base_cost in (5.9,8.5,10.5,null);
select id,base_duration,base_cost,unit_cost from cost where base_cost = (5.9,8.5,10.5,null);
select id,base_duration,base_cost,unit_cost from cost where base_cost in (5.9,8.5,10.5) and base_cost is null;
select id,base_duration,base_cost,unit_cost from cost where base_cost in (5.9,8.5,10.5) or base_cost is null;
