魏老师将两张刚制好的永久装片和两种写明“球形细菌”和“酵母菌”的标签交给你．请你借助电子显微镜下的观察正确地贴好标签．你的依据是（　　）

A．叶绿体的有无

B．细胞壁的有无

C．遗传物质的有

D．细胞核是否成形

Now the weather is becoming ___________ , we should look after ourselves well.

A．cold and cold

B．the coldest and coldest

C．colder and colder

D．colder and coldest