如图为测量滑轮组机械效率的实验装置，钩码总重6N．　　　　　

（1）实验时竖直向上 ____拉动弹簧测力计，由图可知拉力大小为　 ____　N．

（2）若钩码上升的高度为10cm，则有用功是　 ____J，该滑轮组的机械效率为　 ____．

（3）若仅增加钩码的质量，该滑轮组的机械效率将 ____．（选填：“增大”、“减小”或“不变”）

增加: 在缺词处加一个漏字符号(/\),并在其下面写出该加的词。

删除: 把多余的词用斜线(\) 划掉。

修改: 在错的词下划一横线，并在该词下面写出修改后的词。

注意: 1）每处错误及其修改均仅限一词:

2）只允许修改10处，多者(从第11处起) 不计分。

    Mr. Johnson is a hardworking teacher. Every day, he spends too much time with his work. With little sleep and hardly any break, so he works from morning till night. Hard work have made him very ill. “He has ruined his healthy. We are worried about him.” That is which other teachers say. Yesterday afternoon. I paid visit to Mr. Johnson. I was eager to see him, but outside her room I stopped. I had to calm myself down. Quietly I step into the room. I saw him lying in bed, looking at some of the picture we had taken together. I understood that he missed us just as many as we missed him.

观察下面生物体的结构层次概念图，判断下列说法错误的是（　　）

①中央集权制度的建立

②造纸术的发明

③文字和度量衡的统一

④张骞出使西域