Explanation:

- In April 2019, scientists made a significant breakthrough in medical technology by producing the world’s first 3D-printed heart using human tissue.

- Option 1: Croatia - Known for its beautiful coastlines, but not involved in this medical achievement.

- Option 2: Kenya - A country with rich wildlife and culture, but not responsible for this particular innovation in 3D printing.

- Option 3: Ethiopia - Famous for its ancient history, yet not linked with this 3D-printed heart development.

- Option 4: Israel - A nation known for its advancements in technology and medical research. In 2019, Israeli scientists successfully created the first 3D-printed heart using human tissue.