You fly over the sea at FL 90, your true altitude is 9100 ft and QNH is unknown. What can be said about the atmosphere temperature?
a. QNH is lower than standard
b. It is colder than ISA
c. It is warmer than ISA
d. Nothing, insufficient information.
Ans is D. How and why? Is it because Altitude on QNH and ISA Deviation both are unknown?