Who was the developer of the new community of Highlands Ranch
A. Mission Viejo
B. Shea Homes
C. Richmond

A. Mission Viejo

Mission Viejo purchased the property in 1978 for creating the planned community that, the company said, could well be over 50,000 in population within 20 years. Expectations were exceeded, and that number would grow to more than 86,000 by the development's 25th Anniversary in 2006.
Source: Allstar Electrical Serivices

Read about how it all begain in this interview of Mission Viejo's former vice president and director of planning. He talks about purchasing the property in 1978 for $26 million. 
Ranch Planner Toepfer Sits Down for Q&A 
Highlands Ranch Herald posted August 18, 2015