Hello!
Let's go through the given choices to find which word is a synonym for knocking.
A. Rapping means to strike something, specifically hard, loudly, to attract attention.
B. Ticking means to make sharp, short movements like a clock does.
C. Thundering means to make a loud, deep noise.
D. Popping means to make an explosive sound.
Therefore, the answer is A, rapping because knocking is striking a surface to get attention, which is similar to rapping.
As of July 2017, the Ark Encounter company has not released how it is doing financially. Mr Ham who owns and operates the company has declined to provide attendance records or how much has been made. There are numerous news articles stating declining visitors and that the Ark Encounter is failing.
It shows how humans have threatened the life of reptiles while they have lived, by also giving an example of turtles being stuck in the nets. That makes the passage more dramatic and gives the reader an effect of shame, and has left an impact/influence.