[填空题]
A sound wave is traveling in w:x n wi gfw7w-ai+az j6m(hnsq7z-2/karm air when it hits a layer of cold, dense 7*byp0 :,zmqjhhm achkm;5j/air. If the sound wave hits the cold air int:,yaj;b5j0h* chm7p hzm k /mqerface at an angle of 25$^{\circ} $, what is the angle of refraction? Assume that the cold air temperature is $ - 10 ^{\circ} C$. and the warm air temperature is $ + 10 ^{\circ} C$. The speed of sound as a function of temperature can be approximated by v=(331+0.60T) m/s where T is in $ -10 ^{\circ} C$. $^{\circ} $