To measure how Mercury spins, astronomers sent ________ to ...

[DelorasTo]

To measure how Mercury spins, astronomers sent ________ to Mercury and used the Doppler shift to determine how fast it was rotating.
 
  A) probes
  B) laser beams
  C) radar beams
  D) a satellite
  E) a single frequency radio signal

Question 2

The place in a planet's orbit that is closest to the Sun is called:
 
  A) vernal equinox.
  B) aphelion.
  C) perihelion.
  D) crossing the ecliptic.
  E) None of these; a planet's distance from the Sun never changes.

[AISCAMPING]

Answer to Question 1

C

Answer to Question 2

C