A key performance indicator (KPI) is a measurable value that demonstrates how effectively an organisation is achieving a key business objective or critical success factor (CSF). A KPI should be relevant, specific, measurable, achievable, realistic and time-bound (SMART). Therefore, options C, D and E are appropriate KPIs for the CSF ‘provide excellent customer service’, as they measure aspects of customer satisfaction and loyalty that are directly related to the quality of service provided by the hotel chain. Option A is not an appropriate KPI, as it does not measure customer service, but rather customer consumption. Option B is not an appropriate KPI, as it does not measure customer service, but rather customer preference.