Which of the following firearms uses the 5.45x39mm caliber?

The firearm that uses the 5.45x39mm caliber is the AK-74. This caliber was developed in the early 1970s for the Soviet Union's new assault rifle, the AK-74, as a response to the need for a lightweight cartridge that offered improvements over the older 7.62x39mm round used by the AK-47.

The 5.45x39mm caliber provides a flatter trajectory and reduced recoil, which enhances accuracy and allows for more controllable automatic fire. The AK-74 features design elements that are optimized for this round, including a lighter bolt and recoil assembly that accommodate the demands of the lighter ammunition.

In contrast, the AK-47 fires the 7.62x39mm cartridge, the PKM is a general-purpose machine gun that also utilizes the 7.62x54mmR cartridge, and the SVD is a designated sniper rifle that fires the same 7.62x54mmR round. Thus, the characteristics and intended design of the AK-74 directly link it to the 5.45x39mm caliber, making it the correct answer.