左心功能不全发生夜间阵发性呼吸困难的机制是
A．通气功能障碍
B．换气功能障碍
C．呼吸中枢受抑制
D．外周化学感受器调节紊乱
E．酸中毒
参考答案：B
简述苏轼“辞达”的文学观。
Tony eventually realized his childhood dream ___ he could play on one of the top teams.
A．which
B．that
C．of which
D．where
