<prompt> Translate the following text to EnglishUtayari wa kulipa na utayari wa kukubali ni vipimo vinavyoweza kulinganishwa wakati mabadiliko katika ubora wa mazingira ni madogo na kuna mbadala wa karibu zinazopatikana.  <response>: Willingness to pay and Willingness to accept are comparable measures when the change in environmental quality is small and there are reasonably close substitutes available. 