In each of the following sentences, there is a blank space. Below each sentence,there are five words out of which one can be used to fill the blank to make the sentence grammatically and coherently correct. Find the most appropriate word that fit into the blank contextually.

Q:

Tiger populations have been ______for many years due to poaching, loss of habitat, and other human conflicts.

• 1
  declining
• 2
  declined
• 3
  decline
• 4
  declines
• 5
  None of the above