Select unique rows from SQL with exclude some rows Mvc c#

I have a table that I need to select a number of unique rows, but I want to exclude the rows with the same id which are saved in another table.

My first attempt is to select rows which saved before

var QuestionsAnswered = await _context.answers
                                  .Where(e => e.Userid == Userid)
                                  .Select(a => new
                                               {
                                                   Qid = a.Questionid
                                               }) .ToListAsync();

My return is

return View(await _context.questions 
                      .OrderBy(x => Guid.NewGuid())
                      .Take(10)
                      .ToListAsync());

what i have done is

   var QuestionsAnswered = await _context.answers
                                      .Where(e => e.Userid == Userid)
                                      .Select(a => new
                                                   {
                                                       Qid = a.Questionid
                                                   }) .ToListAsync();

 var AllQuestions =   await _context.questions.ToListAsync();


                foreach (var qid in AllQuestions)
                {
                    int QuestionValueId = qid.QuestionId;

                    foreach (var item in QuestionsAnswered)
                    {
                        if (item.Qid == QuestionValueId)
                        {
                            AllQuestions.RemoveAll(a => a.QuestionId == QuestionValueId);

                        }
                    }

but no sense