During the space race on April 12,1961,Soviet cosmonaut Yuri A Gagarin became the first human in space. Seven years later on July 20,1969 the United States responded by - A. sending a man to the moon B. establishing a quarantine against Cuba C. conducting air shipments of vital supplies to East Berlin D. enforcing a ban on military aid to com munist forces in North Vietnam

The correct answer is A. sending a man to the moon.<br /><br />On July 20, 1969, the United States responded to the Soviet Union's achievement of sending the first human, Yuri Gagarin, into space by successfully landing the first humans on the moon. This event, known as the Apollo 11 mission, marked a significant milestone in the space race between the United States and the Soviet Union.