A) they are able to hold their charge for long periods of time without recharging This is the correct answer. Nickel-cadmium (NiCd) batteries are superior to lead-acid batteries for standby service because they can hold their charge for much longer periods of time without needing to be recharged. This makes them ideal for backup power applications where the battery may sit idle for extended periods but needs to be ready to provide power when needed. In contrast, lead-acid batteries tend to self-discharge more quickly, requiring more frequent recharging to maintain their readiness. The other options are incorrect because they do not fully capture the key advantage of NiCd batteries for standby service, which is their ability to hold a charge for long durations.