This topic examines the knowledge of dialectics. Wang Ji's famous phrase "cicadas make the forest quieter, and the sound palace mountain quieter" reflects that the two sides of the contradiction are both opposite and unified. AD embodies the particularity of contradiction, and the specific problems are analyzed in detail; B reflects the qualitative change caused by quantitative change; C embodies the existence and non-existence, and the contradiction between difficulty and easy is the unity of opposites, so C is chosen.