A LAN switch is an intelligent Data Link Layer (Layer 2) device. Unlike an old hub, which simply repeats every incoming bit out of all ports and forces all devices to share one collision domain, a switch makes forwarding decisions based on the Ethernet frame's MAC addresses. This is why the correct answer is that switches improve efficiency by forwarding frames selectively using MAC addresses.

How a switch achieves this:

• It builds and maintains a MAC address table (CAM table) by learning the source MAC address of each frame and the port it arrived on.
• When a frame arrives, it reads the destination MAC, looks it up, and forwards the frame only to the port where that device is connected (unicast) instead of flooding every port.
• Each switch port forms its own collision domain, so devices can communicate in parallel, often in full-duplex mode with no collisions.

The result is that each link carries mostly its own intended traffic, giving higher effective throughput and far fewer collisions.

Why the other options are wrong:

• Broadcasting all frames to every device describes hub behaviour, which wastes bandwidth — it is the very inefficiency switches were designed to eliminate (a switch floods only for unknown-unicast or genuine broadcast frames).
• Increasing collisions and retransmitting is the opposite of a switch's purpose; by segmenting collision domains it reduces collisions.
• Converting digital to analog signal is the function of a modem, not a switch, and has nothing to do with frame forwarding.