Question 15: Forests ___ if deforestation continues.
Answer: C. will be destroyed
(If deforestation continues, forests will be destroyed is the most fitting choice.)

Question 16: We can contribute to a cleaner planet by living ___.
Answer: A. a difference
(We can make a difference by living in a way that reduces pollution.)

Question 17: Our school ___ an event to raise awareness about environmental issues.
Answer: B. will organise
(This sentence refers to a future action, so "will organise" is appropriate.)

Question 18: We ___ more to protect the environment.
Answer: D. will recycle
(This is about a future action that we need to do more often.)

Question 19: Simple actions like recycling and reducing plastic use can ___ a big impact.
Answer: A. cause
(These actions can "cause" a big positive effect on the environment.)