如图所示的向日葵图案是用等分圆周画出的,则⊙O与半圆P的半径的比为( )
A:5﹕3
B:4﹕1
C:3﹕1
D:2﹕1
将铁丝放在空气中无论怎样加热,铁丝只是发红,不会燃烧,而将烧红的铁丝放在盛氧气的集气瓶内,它就会火星四射,剧烈燃烧,下列解释正确的是( )
In our school library there ____________ a number of books on science, and in these years the number of them ____________ growing larger and larger.
____