Answer:
B) Friction
Explanation:
Friction is a force that acts when an object is sliding along a surface. Microscopically, this force is due to the fact that the two surfaces are not perfectly smooth, but they have "imperfections" that cause a force that opposes the motion of the object.
For an object sliding on a flat surface, the force of friction has magnitude:

where
is the coefficient of kinetic friction
m is the mass of the object
g is the acceleration of gravity
The direction of the force of friction is always opposite to the direction of motion of the object.
In reality, friction also acts if the object is at rest and it is pushed by a force; in this case, we talk about static friction, and its magnitude is

where
is called coefficient of static friction, and it is generally larger than the coefficient of kinetic friction.
Answer: I am pretty sure that you should pick radio waves.
Explanation: The scientist should use radio waves. I think this because you can use the radio waves to analyze the signals from outer space. This will work much better than anything there, to analyze it the best possible.
The best I could do.
Answer:
Fundamental frequency in the string will be 25 Hz
Explanation:
We have given length of the string L = 1.2 m
Speed of the wave on the string v = 60 m/sec
We have to find the fundamental frequency
Fundamental frequency in the string is equal to
, here v is velocity on the string and L is the length of the string
So frequency will be equal to 
So fundamental frequency will be 25 Hz