The correct answer is 3.
To break a layer into multiple segments, it takes a device operating at the next layer. In this case, a collision domain is a Layer 1 thing, so it takes a Layer 2 device. In the previous list, all devices, except the bridge, are Layer 1 devices. The bridge is the only Layer 2 device, and every port on a bridge is a separate collision domain and helps reduce the number of collisions. If you only had one device per bridge port, you could then configure full duplex and completely eliminate collisions.