The correct answer is A. GSTR-1.
GSTR-1 is the first return filed under GST. It is a monthly return that must be filed by all registered taxpayers. The return must be filed by the 10th of the following month.
GSTR-1 is a summary of all the sales and purchases made by the taxpayer in the previous month. It includes details of the goods and services sold, the value of the sales, the taxes collected, and the taxes paid.
GSTR-1 is an important return as it is used to calculate the GST liability of the taxpayer. It is also used to reconcile the sales and purchases made by the taxpayer.
The other options are incorrect as they are not the first return filed under GST.
GSTR-2 is a quarterly return that must be filed by all registered taxpayers. It is a reconciliation of the sales and purchases made by the taxpayer in the previous quarter.
GSTR-3A is a monthly return that must be filed by registered taxpayers who are suppliers of goods and services. It is a summary of all the outward supplies made by the taxpayer in the previous month.
GSTR-3B is
a monthly return that must be filed by registered taxpayers who are recipients of goods and services. It is a summary of all the inward supplies received by the taxpayer in the previous month.