某商品的标价为200元，8折销售仍赚40元，则商品进价为（     ）元．

一个边长为0.1m、密度为2×10³kg/m³的均匀正方体置于水平地面上。求：

（1）正方体的质量____ m。
（2）正方体对地面的压强____ P。
（3） 为了改变正方体对地面的压强，小明和小华同学设想沿竖直方向切去任意厚度A，如图(a)所示，并将其分别置于剩余部分的下面或上面，如图(b)、(c)所示。小明认为图(b)的放法可使压强减小，小华认为图(c)的放法可使压强增大。

请判断，小明的设想是____ 的，小华的设想是____ 的。(填“正确”或“错误”)

       A                                                      B

How are you?____                    A. Yes, it is.

What is this in English?____      B. They are in the pencil case.

What color is it?____                C. She is my sister.

Is Tom your brother?____         D. No, they aren't.

where are the pens?____          E. It's red.

Are those his parents?____       F. Green.

What's her family name?____     G. It's a dictionary.

Happy birthday to you!____      H. Yes, he is.

Is this his ruler?____                  I. I'm fine, thanks.

Who is she?____                      J. Thank you.

用反证法证明：在同一圆中，如果两条弦不等，那么它们的弦心距也不等．