固定桥修复的生理基础是（）
A.牙槽骨
B.牙槽嵴黏膜
C.基牙代偿力
D.牙周储备力及代偿功能
E.以上均不是
参考答案：D
仅在体内有抗凝血作用的药物是（）
A.肝素
B.华法林
C.达比加群酯
D.尿激酶
E.阿哌沙班
Which of the following most accurately describes the shape of the average fixed cost (AFC) curve The AFC curve:（）
A. is always below the average variable cost curve.
B. has the same shape as the average total cost curve.
C. becomes flatter as output increases.
