Explanation:

- Option 1: "has added the news of the locust attack into the region"

- This option incorrectly uses "into" and changes the tense, making the sentence less clear.

- Option 2: "had added since the news of the locust attack in the region"

- This option complicates the sentence unnecessarily and changes the meaning.

- Option 3: "added that the news of a locust attack in the region"

- Correctly inserts "that" to make the sentence clear and grammatically sound.

- Option 3 is the correct answer.

- Option 4: "no improvement"

- The original sentence is missing "that," so it needs improvement.