What is the central idea of this paragraph? the code book

What is the central idea of this paragraph? Breaking RSA code is the greatest challenge for cryptanalysts. One of the author's purposes in The Code Book is to explain different types of codebreaking to his readers.

answer; (d) i believe the best answer is ; ///people said that man could not fly, but in 1903, orville and wilbur wright made the first sustained powered flight in a heavier- than-air machine;

earthquake is the answer i remember doing this last year