黄土高原生态环境 ，在经受人类活动破坏后，很难恢复。
脆弱
Not only China but also other countries _____ trying to develop their own economy.[ ]
A. is
B. are
C. has
D. be
患者，40岁，肝硬化大量腹腔积液，呼吸困难，用利尿剂后小便仍少，如需放腹腔积液。放腹腔积液加输白蛋白，每次放多少腹腔积液合适（）
A.<500ml
B.1500.2000ml
C.2500～3000ml
D.4000～6000ml
E.6000～8000ml
