How do musical instruments vary pitch

Higher notes have tighter strings, lower notes have looser strings.

With air operated instruments the lower the space for air to go through the higher the pitch. That's why a tuba has such a low note- because it is very large and wide.

by increasing the amplitude of standing waves

by changing the frequency of standing waves

by interrupting sound waves

by changing the wave length of standing waves

a, c, d, e are all applying about success strategies.