5.32歲的林先生為HBV carrier。在兩週前因兩手第II 及第III指的PIP和 MCP及左手睕關節疼痛到醫院求診。抽血發現ESR=34 mm/1h, CRP=1.87mg/ml, RF=28.4U/ml (normal＜20U/ml)。醫師懷疑為類風濕關節炎，為作鑑別診斷，請問下列的何種檢查最有幫助？
(A)Bilateral hands X-film (AP and Lat. view)
(B)Synovial fluid examination
(C)Soft tissue sonography
(D)Serum anti-CCP antibody
(E)Serum IgG4