与颅内病变有关的疼痛是哪一型（）
A.原发性三叉神经痛
B.继发性三叉神经痛
C.蝶腭神经痛
D.偏头痛
E.神经官能症性头痛
参考答案：B
21. In recent years _____ global warming is becoming ____concern for people all over the world.
A．the; the
B．/; a
C．/; /
D．the; /
重心规则
