— Is there any better way to help my son get rid of the habit of playing computer games?

— To tell you the truth, it's very hard. But we      on this problem to improve the situation.[      ]

A. were working

B. had worked

C. are working

D. had been working

患者男性，38岁。劳力性气促伴心前区疼痛两年。既往有原因不明发热。体检：T：37.5℃，P：92次/分，R：30次/分，BP：125/85mmHg。无发绀，胸骨左缘二、三肋间可闻及Ⅲ级粗糙收缩期杂音及其相连的舒张期杂音，可触及收缩期震颤，肺动脉瓣区二心音亢进，血白细胞12.0×10，中性粒细胞0.87，血红蛋白105g/L，X线胸透见心影略大，左肺门上方有一约6×6cm可与主动脉分离的搏动性肿物，肿物前外方可见钙化。

提示：术中缝闭未闭的动脉导管，切除肺主动脉瘤并行人工血管肺主动脉置换术，术后患者恢复良好。肺主动脉瘤的可能病因是什么（）

A.细菌感染

B.真菌感染

C.梅毒感染

D.不伴先心病的菌性心内膜炎

E.静脉内滥用药物及药（毒）瘾

F.先天性心血管疾病

G.后天性心血管疾病

H.肺动脉高压

I.损伤

J.动脉粥样硬化