In the total time of the United States space program, how many space flight tragedies have occurred? A(1B)2C)NoneD)5help me pls

In the total time of the United States space program, how many space f

1.	In the total time of the United States space program, how many space flight tragedies have occurred? A(1B)2C)NoneD)5help me pls
Answer» tion:Since the 1960S, spaceflight missions have resulted in the accidental deaths of more than 20 astronauts. The most recent disaster, occurring near the end of the SPACE shuttle Columbia's STS-107 mission in 2003, CAUSED NASA to GROUND its shuttle program for more than two years.