Because of how it's worded the answer would most likely be number four
Neglecting friction and air resistance, the first hill must be built 4 times higher than it is now.
The answer would be D, electromagnetic waves
A) 
The total energy of the system is equal to the maximum elastic potential energy, that is achieved when the displacement is equal to the amplitude (x=A):
(1)
where k is the spring constant.
The total energy, which is conserved, at any other point of the motion is the sum of elastic potential energy and kinetic energy:
(2)
where x is the displacement, m the mass, and v the speed.
We want to know the displacement x at which the elastic potential energy is 1/3 of the kinetic energy:

Using (2) we can rewrite this as

And using (1), we find

Substituting
into the last equation, we find the value of x:

B) 
In this case, the kinetic energy is 1/10 of the total energy:

Since we have

we can write

And so we find:

Answer:
Density of the object = 1.9399g/mL
Explanation:
Mass of object = 10.01g
Volume of water = 3.90mL
Volume of Object + Water = 9.06mL
Therefore, volume of Object = Volume of Object + Water - Volume of Water
= 9.06mL - 3.90mL
= 5.16mL
Density by definition is the mass per unit volume of a substance.
Density of the object = mass/volume
= 10.01/5.16
= 1.9399g/mL or 1.94kg/m3