Explanation:

• Callable bonds give the issuer the right to redeem the bond before maturity. When interest rates decline, issuers can call existing higher-coupon bonds and refinance at lower rates, reducing their interest expense.
• Putable bonds benefit the investor, who can put (sell) the bond back to the issuer if rates rise.
• Extendible bonds typically benefit investors by allowing them to extend the maturity.

Therefore, callable bonds benefit issuers when interest rates decline.