种子的胚由下列哪种结构发育而来的( )
A:胚乳
B:卵细胞
C:受精卵
D:受精极核
如图所示,a、b是两种物质质量与体积的关系图象,分别用a、b两种物质制成体积相等的甲、乙两实心物体,浸没在水中.松手稳定后( )
如图,甲、乙两部分相比,( )
Our geography teacher told us to _____ more information about our city and share it next week.