Answer : 4. "ए. एच. टेलर एवं लियो सी. यंग"
Explanation :

A. H. Taylor and Leo C. Young were American scientists who played a crucial role in the development of radar technology. They are credited with creating the first radar system in the United States. Radar, which stands for "Radio Detection and Ranging," is a technology that uses radio waves to detect and locate objects. It became essential during World War II for various applications, including aircraft detection and navigation. The work of Taylor and Young contributed significantly to the advancement of radar technology and its subsequent widespread use in military and civilian applications.