even though she was mocking all the time, she was persistent to support her theory nonetheless AND she did not care of the mockeries

D is the best.

Even though subjected to constant joking

you can write the sentence as below

she was unwavering in advocating her theory, claiming to be untroubled by the raillery, although subjected to raillery

only Japery matches with raillery. both means Joke.

in many cases, you can make yourself some easy examples.

Like

Although she was rejected in her first trial, she came first in her 5th attempt, despite facing many rejections.

ricky05 Why not rebuttal?

the last word given is raillery which means teasing or joking. rebuttal means disprove. it does not fit in the meaning

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