Answer: D. They are the coldest stars.
Explanation:
Absolute zero is not about numbers. It's about temperature, and the
motion of molecules in gases.
You know that the temperature we feel with our skin is the result of the
average speed of all the tiny molecules zipping around or vibrating in
the solid, liquid, or gas.
The faster they're all moving, the warmer the substance feels to us.
The slower they're all moving, the cooler the substance feels to us.
When molecules slow down to zero and lose all of their kinetic energy,
that temperature is what we call 'absolute zero' ... if they're not moving
at all, then they can't move any slower.
To solve this problem it is necessary to use the conservation equations of both kinetic, rotational and potential energy.
By definition we know that

Where,
KE =Kinetic Energy
KR = Rotational Kinetic Energy
PE = Potential Energy
In this way

Where,
m = mass
v= Velocity
I = Moment of Inertia
Angular velocity
g = Gravity
h = Height
We know as well that
for velocity (v) and Radius (r)
Therefore replacing we have

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Therefore the height must be 0.3915 for the yo-yo fall has a linear speed of 0.75m/s