如图所示是小明设计的一个简易电子身高测量仪的示意图。其中，电源电压恒为6V，保护电阻R₀=20Ω；R是一只固定着的、竖直放置的硬电阻棒、总长为40cm，其接入电路的电阻与接入电路的棒长成正比；金属杆cd和MP（右端P是滑片）与电路接触良好，电阻不计。小明用该测量仪对小聪、小英和小亮的身高进行了测量，其数据见如表。若已知小英测量时，滑片恰在电阻棒ab的中点位置，根据题中提供的信息可知（　　）

小明将重为3N的石块挂于弹簧测力计的下端，先后浸没到水和盐水中，石块静止时弹簧测力计的示数如图所示，测石块在水中所受的浮力为____N。图示现象表明，石块所受浮力的大小与液体的____有关，剪断图甲中的细线，石块将____（选填“上浮”、“悬浮”或“下沉”）。

225与50的和是____?其结果除以25，商是____?

下面漫画《扶与不扶》(作者：张吉亮)给我们的哲学启示有（   ）

    Have you ever wondered about the secret life of the tasty lobster(龙虾)？In the sea, it is yellow, orange, grey, green, brown or even blue. Cooking turns it red.

    Lobsters are nocturnal creatures(夜行物)，so it is best to hunt(捕捉) them at night when they are active. You can catch lobster by hand, but you should wear thick gloves because lobster's claws are strong. A very large lobster could break your finger.

    Interestingly, in the past, lobsters were only served to prisoners as they were considered as a poor man's food. Nowadays, lobsters are an expensive and popular dish.