Answer:
Diffusion rate is 1.96 ×
/s
Explanation:
Diffusion is the process in which the molecules of a substance propagates from a region of higher concentration to region of lower concentration through a semi-permeable membrane.
diffusion rate = 
Given that; diameter = 15 mm, time = 15 minutes.
The dye spread in a circular form, so that;
area = 

r =
=
= 7.5 mm = 0.75 cm
area =
×
= 1.7679 
time = 15 minutes = 15 × 60 = 900 seconds
So that;
diffusion rate = 
= 0.0019643
/s
Diffusion rate is 1.96 ×
/s
Your answer is A because B and C don't make sense and D is wrong
The answer is C. organs
organs are a group of different tissues working together to complete a life function
hope this helps