Within one year of its appointment, the charter commission shall submit a report in writing on its activities, findings, and recommendations to the legislative body of the county together with a draft of the proposed charter. The legislative body of the county may in turn propose one or more sections as alternative, or alternatives to any section of the proposed charter; provided that there shall not be more than a single proposition under any alternative proposal. Within thirty days after the receipt of the proposed charter from the commission, the legislative body shall return the proposed charter with the alternatives to the commission for its study.