What property of a wave changes to create the doppler effect?

speed

amplitude

medium

frequency

i really do want to but i just don't know it i'm so sorry : (

the answer that best explains what happened to george washington at fort necessity, pennsylvania is : washington was attacked by the french but was able to negotiate with them to peacefully end fighting. the battle took place on july 3, 1754. the battle is considered as being the start of the french and indian war.

hey hope i can the answer is

1 battles of lexington and concord

2 battle of bunker hill  

3 battles of saratoga

4 battle of new york

5 battle of yorktown

it's a to start a war with the americans