A:(2,3)
B:(-2,3)
C:(1,−12)
D:(-2,0)
Over the past years, scientists have made many great b____ in science and technology.
在植物根尖的结构中,吸收水分和无机盐的主要部位是( )
血液有两种:含氧量高、颜色鲜红的____ 和含氧量低、颜色暗红的____ .