The Travel and Tourism Competitive Index (TTCI) is released by

1. A

   World Bank

   The World Bank publishes Doing Business (now paused) and other indices, not the Travel and Tourism Competitiveness Index.

2. B

   International Monetary Fund

   The IMF publishes the World Economic Outlook, not TTCI.

3. C

   World Economic Forum

   The World Economic Forum releases the Travel and Tourism Competitiveness Index (later Travel & Tourism Development Index). That is the official key.

4. D

   United Nations Development Programme

   UNDP publishes the Human Development Report, not TTCI.

Summary. Official key is (c) World Economic Forum. TTCI scores enabling environment, policy, infrastructure and natural/cultural resources. Honour the stored letter (c).