“终于把作业做完了,哈哈!”吴晓宇眉飞色舞地合上作业本,收拾起桌上七零八落的文具。一抬手,他发现右手的手指侧面黑乎乎的。自从改用了钢笔,每回写作业总弄得一手黑。“还是圆珠笔好,干净又方便。”吴晓宇对贾波特说。“对啊!你看钢笔属于水性笔,圆珠笔属于油性笔。当初圆珠笔被发明出来的时候,墨迹干净就是它的一大卖点。”贾波特拆过一支圆珠笔,知道圆珠笔里面有个秘密小滚珠,“发明圆珠笔的人真是聪明,让一颗小珠子来写字。发明它的人是谁?” “Finally finished the homework, ha ha!” Wu Xiaoyu enraged to close the homework, packed up on the desk scattered stationery. As soon as he raised his hand, he found the black finger on the side of his right hand. Since the switch to the pen, always write a black handwriting back homework. “Or ball-point pen is good, clean and convenient. ” Wu Xiaoyu Jia Bote said. “Right ah! You see the pen belongs to the water-based pen, the ballpoint pen belongs to the oil-based pen. When the ballpoint pen was invented, the ink is clean and it is a big selling point.” “Jia Bote split a ballpoint pen, Secret ball, ”The person who invented the ballpoint pen is really clever, let a small bead to write. Who invented it?“ ”