A depression diagnosis is often difficult to make because clinical depression can manifest in so many different ways.

【正确答案】 C

【答案解析】解析：manifest“显示，表明，证明”。intensify“增强，变强”；declare“宣布，声明，声称”：demonstrate“证明，证实，显示”；intimidate“恐吓，威胁”。综合比较各选项，不难看出，只有C项与画线单词的意思完全一致，故选C。