Answer:
Their experimental design lacks control group
Explanation:
Based on what I read, the scientists don't have a control group as one of the main groups thus they cannot, in scientific sense, say that the medicine is better or worse. You always need a control group receiving no intervention because then we can compare groups and assess the effectiveness of that intervention (in our case if we had control group vs people who received the medicine, we could see if the people who received the medicine had improved condition etc when compared to participants who did not receive anything)
The eccentricity of its orbit is 
<h3>What is mass?</h3>
- Mass is a physical body's total amount of matter. It also serves as a gauge for the body's inertia or resistance to acceleration (change in velocity) in the presence of a net force. The strength of an object's gravitational pull to other bodies is also influenced by its mass.
- The kilogram is the SI unit of mass (kg). In science and technology, a body's weight in a given reference frame is the force that causes it to accelerate at a rate equal to the local acceleration of free fall in that frame.
- For instance, a kilogram mass weighs around 2.2 pounds at the surface of the planet. However, the same kilogram mass would weigh just about 0.8 pounds on Mars and about 5.5 pounds on Jupiter.
- An object's mass is a crucial indicator of how much stuff it contains. Weight is a measurement of an object's gravitational pull. It is influenced by the object's location in addition to its mass. As a result, weight is a measurement of force.
The length of the semi-major axis is calculated as follows:
where
mass of sur
- a mass of the comet


To learn more about mass, refer to:
brainly.com/question/3187640
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The answer is d, gravity is the only force acting on the object
The acceleration should 5.4 m/s^2