Synaptic pruning removes connections that go unused, and a child's brain has far more synapses than an adult's. Why is losing connections a form of development rather than decline?

C. Because an over-connected network is inefficient and slow.

The developing brain overproduces synapses and lets experience select among them, sculptural rather than subtractive, since an everything-to-everything network is expensive, slow and poor at discrimination. Infants discriminate every language's phonemes and by twelve months only their own, which is why the Japanese r/l distinction defeats adult English speakers.