Need to add Dropdown in Excel using ASP.NET CORE 2.0

I want to add dropdown list in excel sheet using asp.net core 2.0 application .I am using

using Microsoft.AspNetCore.Hosting;

MemoryStream stream = new MemoryStream();

using (ExcelPackage package = new ExcelPackage(stream))

{

ExcelWorksheet worksheet = package.Workbook.Worksheets.Add("QuesAnsDetails");

I have created list values in dropdown but not able to add list values in run time

var list1 = new System.Collections.Generic.List();

list1.Add("Charlie");

list1.Add("Delta");

list1.Add("Echo");

var flatList = string.Join(",", list1.ToArray());

QuestionAnswerEntity questionAnswerEntity = new QuestionAnswerEntity();

questionAnswerEntity.CallDriverId = 0;

questionAnswerEntity.UserName = string.Empty;

var list = this._iQuestionAnswerBLL.GetQuestionAnswerFormat(questionAnswerEntity);

for (int i = 0; i < list.Count - 1; i++)

{

worksheet.Cells[i + 2, 1].Value = list[i].CallDriverName;

worksheet.Cells[i + 2, 2].Value = list[i].ScenarioName;

worksheet.Cells[i + 2, 3].Value = list[i].LearningActivityId;

worksheet.Cells[i + 2, 4].Value = list[i].LearningActivityName;

worksheet.Cells[i + 2, 5].Value = list[i].Question;

worksheet.Cells[i + 2, 6].Value = list[i].Answer1;

worksheet.Cells[i + 2, 7].Value = list[i].Answer2;

worksheet.Cells[i + 2, 8].Value = list[i].Answer3;

worksheet.Cells[i + 2, 9].Value = list[i].Answer4;

// worksheet.Cells[i + 2, 10].Value = list[i].CorrectAnswer;

worksheet.Cells[i + 2, 10].Value = list1

}