病毒与细菌最明显的区别是( )
A:无成形细胞核
B:没有细胞壁
C:没有细胞膜
D:没有细胞结构
—Can you tell me _______ it is from your home to school?
—It's about three kilometres.
720-20=____ 4×9=____
340-300=____ 38÷7=____……____
580+210=____ 423+300=____
50÷7=____……____ 518-500=____
8×9=____ 732+200=____
(Ⅰ)若t=1,证明x=1是函数f(x)的极小值点;
(Ⅱ)求证:f(x)≥0.
____this cloth ____ ____ silk?