Answer:
A
Explanation:
SInce It is peaking at the top that's where energy is stored
Contact is 'touching'. If a person 'touches' something skins cells, sweat and DNA are left behind. This confirms that a person was present.
Answer:
57.17 Hz 114.34 Hz 285 Hz
Explanation:
The distance between the men and 1 speaker = 3.5 m
Distance between the men and second speaker = 10-3.5= 6.5 m
Here at this point there will be no sound so there will be destructive interference
Path difference 
We know that for destructive interference 

here v is the speed of sound in air
So for m =0

for m =1

for m=2

Two of these choices are correct. The nucleus of the atom has a positive charge, because of the positively charged protons in there.