Cannot implicitly convert dbSet to ObjectQuery

Question

That is my code and it doesn't work like this, please help me !!!

public class BL: IBL, IDisposable
{

    private TradeSoftDBEntities entities;

    public List<Roles> TakeRoles()
    {

        if (entities == null) 
            entities = new TradeSoftDBEntities();

        ObjectQuery<Roles> roles = entities.Rolis;

        roles.MergeOption = MergeOption.NoTracking;