Question 1
Mach number is TAS divided by the local speed of sound. The local speed of sound is proportional to square root of local temperature. As a general rule, (below the tropopause and ignoriing inversions) as you climb it gets colder, so the local speed of sound decreases.
This means that at a constant Mach No. your TAS will be decreasing also.
Above the Trop, and assuming you're not going to reach the mesopause, temperature is pretty much constant so the TAS should stay constant at a given Mach No.
Question 2
True airspeed = exactly what it says.
Equivalent airspeed = what a perfectly working ASI will read, setup for ISA sea-level conditions. For EAS multiply TAS by the square root of relative density.
Calibrated airspeed = EAS plus compressibility errors. Anywhere below 0.5M you can ignore the difference.
Indicated Airspeed = CAS plus system and position errors (known as PEC, Pressure Error Corrections). This is what you actually see on the dial.
It's a more or less universal rule that as you climb, density goes down. So, at anything above sea-level TAS will be bigger than CAS. The higher you climb, the bigger difference.
That was the long answer, the short answer is C.
G