A. Outside on a summer day, there are less particles that the sound bounces off of (snow and wind absorb the sound)
B. Water, sound travels faster through denser objects. Water has a higher density than air.
C. High air pressure, sound moves faster through matter that is closer together. This can be said because sound can't travel through space. (There is no atmosphere and consistent particles in space for sound to go through)
D. A piece of steel, It's denser than wood and water.
E. 90% nitrogen and 10% helium, nitrogen is denser than helium so it will move faster