题干
Some visit the Great Wall every year．
A：visiter
B：visitor
C：visitors
D：visiters
答案(点此获取答案解析）
C
Some visit the Great Wall every year．
A：visiter
B：visitor
C：visitors
D：visiters
分裂的后期，纺锤丝牵引染色体移向细胞两极，直接提供能量的物质是（ ）