Why has NASA sent recent orbiters to Mars on trajectories that required them to skim through Mars's atmosphere before settling into their final orbits?

Question

A) It saves money because the spacecraft uses atmospheric drag to slow down rather than needing to carry enough fuel to slow by firing rocket engines.
B) It allowed the orbiters to get higher resolution pictures of the surface as it came close when skimming through the atmosphere.
C) It allowed the spacecraft to collect samples of the atmospheric gas for return to Earth.
D) Each spacecraft also carried a lander, and the lander could only be dropped to the Martian surface when the spacecraft passed through the atmosphere.

Answer 1

A) It saves money because the spacecraft uses atmospheric drag to slow down rather than needing to carry enough fuel to slow by firing rocket engines.