短語詞組短語twofold purchase 雙倍復滑車twofold advantage 雙重好處twofold classification 雙重劃分twofold action 雙重作用twofold integration 二重積分twofold whirl 復合旋流twofold integral 二重積分twofold connotation 兩重涵義 返回 twofold