They are dynamic, with winds and waves constantly reworking and moving
the barrier island sand.
Changes in sea level also affect these islands.
Most scientists agree that sea level has been gradually rising over the
last thousand years, and this rise could be accelerating today due to global warming.
Rising sea level causes existing islands to migrate shoreward.
To solve this problem we will apply the concepts related to the calculation of the speed of sound, the calculation of the Mach number and finally the calculation of the temperature at the front stagnation point. We will calculate the speed in international units as well as the temperature. With these values we will calculate the speed of the sound and the number of Mach. Finally we will calculate the temperature at the front stagnation point.
The altitude is,

And the velocity can be written as,


From the properties of standard atmosphere at altitude z = 20km temperature is



Velocity of sound at this altitude is



Then the Mach number



So front stagnation temperature



Therefore the temperature at its front stagnation point is 689.87K
C is correct answer.
Walking along a 6 meter beam without falling helps to develop balance.
Hope it helped.
-Charlie