how do return this nvarchar to c#

set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
go

ALTER PROCEDURE [dbo].[TOP_Returner]
    (@number [bigint],
     @return_top nvarchar(200) output
    )
AS
declare @top_name nvarchar(200)

if @number=1
begin
select  top (1) @top_name=[product_name] From View_Product_4_TopBest
set @return_top=@top_name
return @return_top
end

if @number=2
begin
select top (1) @top_name=[color_name] From View_Color_2_TopBest
set @return_top=@top_name
return @return_top
end

if @number=3
begin
select top (1) @top_name=[model_name] From View_Model_2_TopBest
set @return_top=@top_name
return @return_top
end

if @number=4
begin
select top (1) @top_name=[size_name] From View_Size_2_TopBest
set @return_top=@top_name
return @return_top
end

if @number=5
begin
select top (1) @top_name=[group_name] from View_ProductGroup_TopBest
set @return_top=@top_name
return @return_top
end