致密下层中锚原纤维的主要成分是（）
A.Ⅳ型胶原
B.Ⅲ型胶原
C.Ⅶ型胶原
D.Ⅷ型胶原
参考答案：C
Which of the following is NOT a cause of increasing decline of wild animal population
A．Exploitation.
B．Pollution.
C．Habitat alteration.
D．Congressional law.
