Mr Brown gave me a very valuable present, ________that I have never seen.
A:the one
B:it
C:one
D:which
下图是植物细胞与动物细胞示意图,请据图作答:
They saw the missing boy ______ near the river at that time.
离体的叶绿体在光照下进行光合作用时,如果突然中断CO2的供应,短暂时间内叶绿体中三碳化合物与五碳化合物相对含量的变化是( )
根据心脏结构和人体血液循环示意图,回答下列问题: