//you can assign conditions flexibly
List<string> listTemp = new List<string> { };
listTemp.Add( "B" );
listTemp.Add( "C" );
listTemp.Add( "D" );
listTemp.Add( "E" );
listTemp.Add( "F" );
dt_thk = dt_raw.AsEnumerable( )
.Where( Row => listTemp.Contains(Row.Field<string>( "A" )))
.CopyToDataTable( );