what is the most fuel efficient diesel engine?
['Kia Ceed 1.6 CRDi (Official fuel economy - 72.4mpg) ... ', 'Citroen C4 Cactus 1.6 BlueHDi (Official fuel economy - 70.6mpg) ... ', 'Vauxhall Corsa 1.3 CDTI (Official fuel economy - 78.5mpg) ... ', 'Renault Clio 1.5 dCi (Official fuel economy - 70.6mpg) ... ', 'Mercedes-Benz A Class A180d (Official fuel economy - 80.7mpg)']