______ is a good girl. [ ]
A. Michael
B. Colin
C. Walter
D. Tina
答案:D
致密骨岛一般可呈圆形或卵圆形,其直径多为()
A.1~2cm
B.2~4cm
C.3~4cm
D.4~5cm
E.4~6cm
根尖由哪几部分构成?各部分细胞有何特点?