The Reason for the Surprising Result Measured by the Viking

Multiple Choice

The reason for the surprising result measured by the Viking Lander spacecraft on Mars,that the pressure readings of the atmosphere seemed to go down continuously after the spacecraft landed,is that

A) the sensors were measuring outgassing of the spacecraft as it adjusted to the very low atmospheric pressure on Mars.
B) the sensors were slowly deteriorating in the intense solar UV radiation,making them progressively less sensitive.
C) the major constituent of the atmosphere,CO₂,was freezing into dry ice flakes as winter approached.
D) the wake caused by the landing of the spacecraft acted like a hole in the atmosphere to allow the surface gases to escape.