how to use distinct in linq query in c#

public static IQueryable<ProdType> GetDistinctProdType(
    this IQueryable<ProdInfo> query,
    int categoryId)
{
    return (from p in query
            where p.CatID == categoryId
            select p.Type).Distinct();
}

var uniquePeople = from p in people
                   group p by new {p.ID} //or group by new {p.ID, p.Name, p.Whatever}
                   into mygroup
                   select mygroup.FirstOrDefault();