Complete the sentence.
Despite our best efforts to protect the environment and keep it safe, until the problems of pollution are _______, the future of our environment seems, at best, _______.

Despite is a clue that the sentence sets up a contrast. We want to keep the environment safe, but there are problems with pollution. The first blank requires a word that tells what we want to do about the problems of pollution. The best choice is to end them or solve them as in choice (Solved . . . Uncertain). Until those problems can be solved, the future of the environment is not safe, but rather uncertain.