Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct option that best fits each of the numbered blanks from 18 to 22.

Conservation centres play a crucial role in nurturing endangered animals before reintroducing them into their natural habitats. These centres, which specialise in the care and rehabilitation of threatened species, ___(1)___. This process ensures that the animals are strong enough to survive in the wild.
Releasing these animals back into the wild, however, presents many challenges. One major issue is that animals ___(2)___ may struggle to adapt to their natural habitats. For example, they might not know how to hunt or find food independently, skills essential for survival. As a result, ___(3)___. Additionally, conflicts with existing wild populations can occur, as territorial disputes may arise.
Despite these difficulties, the efforts are worthwhile. Reintroduced to natural habitats, ___(4)___. Successful cases, such as those involving large predators like wolves or big cats, have proven that with thorough planning, conservation projects can contribute to healthier environments. In conclusion, ___(5)___.