A．With the help of PSAs, the ground crews and scientists can present in real time in the spacecraft.
B．With the help of PSAs, the ground crews and scientists can control the spacecraft as if they were there.
C．With the help of PSAs, the ground crews and scientists cannot in real time present in the spacecraft.
D．With the help of PSAs, the ground crews and scientists cannot advise the astronauts to deal with different situations.