Quarterly return eligibility clarified; eligible registered persons may file quarterly returns and pay taxes monthly under conditions. Notification permits registered persons below a specified aggregate turnover threshold to furnish returns quarterly while paying tax monthly, subject to the preceding month's return having been filed; once the option is exercised it continues until revised. Exceeding the turnover threshold during a quarter disqualifies a person from quarterly filing from the first month of the next quarter. The notification also prescribes deemed options for sub-classes based on prior GSTR-1 filing frequency and allows electronic change of the default option on the common portal during a prescribed window.