According to the following introduction of President Ronald Reagan's speech honoring the memory of the seven astronauts killed in the Space Shuttle Challenger explosion, why was “Shuttle Mission 51-L” considered to be historic and different from other space flights? Officially, it was "Shuttle Mission 51-L," but every American knew it as "the flight with the teacher" because one of the crew members was a thirty-seven-year-old teacher named Christa McAuliffe. The first civilian to venture into space, McAuliffe had been chosen out of 11,000 volunteers to join six astronauts on the space shuttle Challenger. Promising "the ultimate field trip," NASA1 heavily promoted the launch, and tens of millions of Americans—many of them schoolchildren—tuned in to witness the historic event live on January 28, 1986. At 11:39 A.M., cheers erupted at Cape Canaveral and at McAuliffe's school back in Concord, New Hampshire, as the Challenger soared skyward into a picture-perfect, cloudless sky. And then suddenly, inconceivably, the shuttle disappeared into a massive fireball as the two booster rockets sailed on, leaving behind a billowy pitchfork of smoke. Shock immediately turned to grief as the realization sank in: The shuttle had exploded, killing everyone on board. President Reagan was scheduled to give the State of the Union address before Congress that evening, but instead focused solely on the seven crew members who lost their lives—the first American astronauts ever to die in flight.
A. It included the first female astronaut
B. It included the first private citizen
C. It was the first time a space shuttle was launched
D. It was the first time astronauts planned to walk in space