Answer:
C) Dog: 40 kg, Medicine: 1.6 mL
D) Dog: 35 kg, Medicine: 1.4 mL
Step-by-step explanation:
we know that
A relationship between two variables, x, and y, represent a proportional variation if it can be expressed in the form
or 
Let
x ---> the mass, in kilograms of a dog
y ---> milliliters of flea medicine a veterinarian prescribes
<u><em>Find the value of the constant of proportionality k for the given data</em></u>

For x=50 kg, y=2 mL ----> 
For x=10 kg, y=0.4 mL ----> 
For x=5 kg, y=0.2 mL ----> 
so
The linear direct equation is equal to

<u><em>Verify each choice</em></u>
A) Dog: 15 kg, Medicine: 0.9 mL
Divide the milliliters of medicine by the kilograms of the dog and compare the result with the constant of proportionality

so

therefore
These numbers could not be used as the missing values in the table
B) Dog: 25 kg, Medicine: 0.8 mL
Divide the milliliters of medicine by the kilograms of the dog and compare the result with the constant of proportionality

so

therefore
These numbers could not be used as the missing values in the table
C) Dog: 40 kg, Medicine: 1.6 mL
Divide the milliliters of medicine by the kilograms of the dog and compare the result with the constant of proportionality

so

therefore
These numbers could be used as the missing values in the table
D) Dog: 35 kg, Medicine: 1.4 mL
Divide the milliliters of medicine by the kilograms of the dog and compare the result with the constant of proportionality

so

therefore
These numbers could be used as the missing values in the table
E) Dog: 20 kg, Medicine: 1.2 mL
Divide the milliliters of medicine by the kilograms of the dog and compare the result with the constant of proportionality

so

therefore
These numbers could not be used as the missing values in the table