Which combination correctly describes the first Bitcoin halving in 2012?

Detailed explanation

Bitcoin's first halving took place in 2012 at block height 210,000. New issuance permitted under the rules fell from 50 to 25 BTC per block. This began the next stage of the predetermined issuance schedule.

The block subsidy was halved. Existing balances did not change, and transaction fees were not halved by the same rule. The figure of 25 BTC therefore describes the subsidy for that period, not a permanent total payment to miners.

The event is defined by block height. The approximate interval between halvings depends on how quickly blocks are found. A halving is therefore a change within the predetermined issuance schedule, not a later cut to existing balances.