Explanation:

- The sentence talks about a mysterious illness affecting dogs in Norway.

- Option 1: Desperate doesn't fit well because "desperate" describes a feeling of hopelessness or urgency, not an illness.

- Option 2: Suspicious could imply the nature of the illness is questionable, but it doesn't describe the severity of the illness.

- Option 3: Dreary usually refers to something dull or depressing, and it doesn't convey the seriousness of an illness.

- Option 4: Fatal refers to causing death, which aligns with the most serious consequence of an illness mentioned as "at times" implying sometimes leading to death.

- Correct Answer: Option 4 - Fatal

"Fatal" is the best choice as it accurately describes an illness that can result in death.