Waves will have the highest speed in at 0°cair at 5°cair at 20°cair at 30°c

The answer is air at 30oC . This is because air at 30oC has its molecules vibrate faster  than at lower temperatures. Waves travel faster in molecules that are highly excited together than less excited. Sound may seem to travel further in cold air because the warm air above it refracts sound waves, at the boundary of the two air masses, back to the cold air hence its traveles greater distances.

the plateau is likely to turn into a desert do to corrosion.

b. latent learning (the word "latent" itself means something that exists but isn't obvious, only under certain conditions! )