I think it’s C. If not I’m sorry
It takes nd/ (lambda*f) time or a short pulse of light to travel from one end of the glass to the other.
If we talk about free space, that is, vacuum, light travels at a speed of 3x10^8 m/s, yet inside a glass light travels at a speed of v= c/n, where v is the velocity of the light and n is the refractive index. Now,
v=d/t,
so t= d/v
t= d/ (c/n)= n*d/c
c= lambda*f
t= nd/(lambda*f)
here, d is the thickness of the block, t is the time required and c refers to speed of light.
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A. a law of requiring bike helmets.
D. Islam spread inside and outside the new Arab Muslim Empire.
Answer: Positive externality
Explanation: Positive externality is the concept in which the service produced and the consumption of that service will provide benefit a third party who is not a part of the process.
While producing fertilizer , it is providing a unintentional benefit to the community surrounding(third party) by keeping the insects away through exerting gases so that they don't cause insect bites or other problem.
Other options are incorrect because negative externalities are negative consequences face by the third party in a process. Comparative externality is related with comparison and pecuniary externality is increment or decrement in market price of service by action of economic actor .