【单选题】Which of the following best describes the relation of paragraph 2 to paragraph 1?
A.
Paragraph 2 shows how the problem discussed in paragraph 1 arose.
B.
Paragraph 2 explains how the problem presented in paragraph 1 came to be solved.
C.
Paragraph 2 provides a more technical discussion of the problem introduced in paragraph 1.
D.
Paragraph 2 shows why the problem discussed in paragraph 1 was especially important to solve.