How is outside air temperature measured/calculated?
 

How is outside air temperature measured/calculated in most modern jet aircraft?
A. Outside air temperature is measured directly from the total air temperature probes.
B. Outside air temperature is measured directly from the static air temperature probes.
C. Outside air temperature is calculated based on actual ram air temperature (also known as total air temperature) and the standard atmospheric temperature lapse rate.
D. Outside air temperature is calculated by directly measuring ram air temperature (also known as total air temperature) then subtracting a correction for Mach number.

I would guess D?

D - with the quibble that most formulas I see use TAS^2 instead of Mach number per se, to calculate the correction, which is called "ram rise" and is indeed subtracted from total (static) air temp to get true or ambient temp.

TAT = SAT - RR

Below Mach 0.2, the difference between TAT and SAT is negligible.

Total Air Temperature (aka TAT) is measured directly (sometimes subject to probe error corrections). Static Air Temperature is calculated from TAT and airspeed.
No one has invented a reliable, consistent method of measure Static Air Temperature.