The correct answer is (e). Slovakia reports using a number of different approaches in its CRF tables (see Table Summary 3 of its CRF spreadsheets). In earlier years, Slovakia relied on the reference approach for some estimates. As discussed in Slovakia’s National Inventory Report (NIR), the sectoral approach was implemented using a different data set starting in 2000, which was again revised in 2004. Little information is provided to explain what methods or data were used prior to 2000. There is not sufficient information provided to determine if the data sources and methods are in accordance with the IPCC Good Practice Guidance for maintaining consistency across time series (see Section 7.3.2.2, p. 7.19 of the IPCC Good Practice Guidance). For non-road transport, fuel consumption was estimated using LTOs for aircraft and shipping activity for watercraft.