At a bond's maturity date:

• the issuer has 30 days to re-pay the principal balance
• the issuer must make a coupon payment
• the issuer is obligated to retire the bond by repaying the bondholder in full and with any past due interest
• bondholders automatically convert the bond to equity
• all of the above
• none of the above

The question is saying to choose all options that apply, so what happens at a bond's maturity date?