The correct answer is: C. Radio Shack
Radio Shack was the first firm to mass-market a microcomputer as a personal computer. In 1977, they released the TRS-80, which was one of the first affordable and easy-to-use personal computers. The TRS-80 was a huge success, and it helped to popularize the personal computer revolution.
IBM was a major player in the computer industry in the 1970s, but they did not release their first personal computer until 1981. The IBM PC was a very successful computer, but it was not the first personal computer to be mass-marketed.
Sperry Univac was another major player in the computer industry in the 1970s. They released their first personal computer in 1978, but it was not a commercial success.
Data General Corporation was a computer company that was founded in 1968. They released their first personal computer in 1981, but it was not a commercial success.
In conclusion, the first firm to mass-market a microcomputer as a personal computer was Radio Shack.