I would probably reduce the number of quotes by simplifying the expression
SELECT ",2,4,7,16,27,35," AS Chuoi,
IIf(InStr([Chuoi],"," & Val([C1]) & ",") >0,[C1],Null) AS A1,
IIf(InStr([Chuoi],"," & Val([C2]) & ",") >0,[C2],Null) AS A2,
IIf(InStr([Chuoi],"," & Val([C3]) & ",") >0,[C3],Null) AS...