Massive MIMO antenna arrays is the correct option.

Massive MIMO antenna arrays use a very large number of antennas at the base station which allows simultaneous spatial multiplexing of many users on the same time and frequency resources. This increases spectral efficiency and cell capacity and it enables narrow beamforming that improves link quality and energy efficiency. Those physical layer gains are the primary reason 5G delivers substantially greater capacity and more efficient data transfer compared to 4G.

Channel bonding can increase throughput by combining channels but it is not the defining 5G advancement that provides the large capacity and spectral efficiency improvements. Channel bonding is more common in Wi Fi and other link aggregation contexts and it does not deliver the same spatial multiplexing benefits as massive MIMO.

Network slicing is a 5G capability that creates multiple virtual networks on the same physical infrastructure to provide service isolation and custom performance. It improves flexibility and management but it does not directly increase radio spectral efficiency or raw physical layer capacity.

Packet switching is the fundamental method for carrying user data in modern networks and it was already used in 4G. It is not a new 5G technology that explains the substantial capacity gains between 4G and 5G.

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