With a lot of problem ________, the newly-elected president is having a hard  time. [ ]

A. settled

B. settling

C. to settle

D. being settled

嘌呤核苷酸分解代谢的终产物是

A．尿酸

B．次黄嘌呤

C．黄嘌呤

D．β-氨基异丁酸

E．CO₂＋H₂O