Our order was for paper, ribbons and envelopes but you sent only

Our order was for paper, ribbons and envelopes but you sent only paper and envelops.
【正确答案】：envelopes; 或envelopes,
【题目解析】：在一个并列举中，如果其中一个或两个独立主句含有逗号，那么就要在并列连词前用分号。