Which of the following hardware devices prevents broadcasts from crossing over subnets?

A bridge operates at Layer 2 and forwards broadcast frames to all ports within the same network segment, so it does not prevent broadcast propagation across segments.

A hub operates at Layer 1 and repeats all signals including broadcasts to every connected port without any filtering or segmentation.

Routers make forwarding decisions based on IP addresses at the Network layer (Layer 3) and each router interface belongs to a separate broadcast domain. Because routers do not forward broadcast frames between interfaces, they naturally contain broadcasts within the originating subnet and prevent them from propagating to other subnets.

A modem modulates and demodulates signals for transmission over a communication medium and has no capability to filter or segment broadcast traffic.