Which of the following CPU features allows the operating system to see a core as dual processors?

Dual-channel memory is a motherboard/memory controller feature that doubles memory bandwidth between the CPU and RAM; it does not affect how many logical processors are exposed to the OS.

64-bit support extends the addressable memory space and register width for a CPU but does not create additional logical processors.

Hyperthreading works by duplicating the architectural state (registers, instruction pointer) within a single core so the OS schedules two threads simultaneously on one physical core, effectively doubling the logical processor count visible to the OS.

An integrated GPU is a graphics processing unit embedded in the CPU die to handle display output; it has no effect on the logical processor count seen by the OS.