在学过摩擦力知识后，小明想探究：摩擦力大小是否与压力、重力都有关系？他利用如图所示的装置进行探究实验．
实验步骤如下：
①把金属盒放在质量不计的白纸上，读出台式测力计示数；拉动白纸的过程中，读出弹簧测力计的示数．
②将质量不计的氢气球系在金属盒上，读出台式测力计示数；拉动白纸的过程中，读出弹簧测力计的示数．
③再往金属盒注入适量的沙子，使台式测力计示数与步骤①中的示数相等，拉动白纸的过程中，读出弹簧测力计的示数．
实验相关数据如下表：

（1）此实验是根据____原理测出摩擦力大小的．
（2）与直接用弹簧测力计拉动金属盒测量摩擦力相比，拉动白纸进行实验具有容易操作的优点，具体体现在：____ ．（写出一条即可）
（3）请你补齐上表中空格处的数据，其值为____ N.
（4）实验中是通过____ 来改变金属盒总重力的．
（5）比较实验步骤____ （填序号）的数据，说明摩擦力大小与重力无关．

著名的周口店的北京猿人，一般认为其属于(    )

    Some years ago,writing in my diary used to be____usual activity. I would return from school and spend half an hour ____(record)the day's events, feelings, and ____(impress)in my little blue diary. I did not really need ____(express) my emotions by way of words, but I gained a certain satisfaction from ____(see) my experiences forever recorded on paper, After all, isn't accumulating(积累）memories a way of preserving the past?

    ____ I was thirteen years old, I went on a long journey____ foot in a great valley____(equip) with pens, a diary, and a camera. During the trip, I was busy recording every incident, name and place I came across. I felt ____(pride) to be spending my time productively, dutifully preserving for future generations a detailed description of my travels. On my last night there, I ____(walk)out of my tent, diary in hand.