实验室制备硝基苯的主要步骤如下：

①配制一定比例的浓硫酸与浓硝酸的混和酸，加入反应器中．

②向室温下的混和酸中逐滴加入一定量的苯，充分振荡，混和均匀．

③在50﹣60℃下发生反应，直至反应结束．

④除去混和酸后，粗产品依次用蒸馏水和5%NaOH溶液洗涤，最后再用蒸馏水洗涤．

⑤将用无水CaCl₂干燥后的粗硝基苯进行蒸馏，得到纯硝基苯．

填写下列空白：

心血管疾病一直是威胁人类生命的头号杀手，目前针对心脏疾病最有效的办法之一是植入心脏起搏器，其工作原理如图甲所示，由脉冲发生器定时发放电流，通过电极导线传输到电极所接触的心肌（心房或心室），使之受到刺激而产生收缩活动。

阅读下面短文，按要求完成各项任务。

   "Pictogram" is a compound word made from "picture" and "telegram". Pictograms are usually simple pictures, and they are often made with letters and words. A pictogram is a symbol which represents an idea or an object through an image (图像). Also, it is a kind of communication system which must be learned but is very useful in our lives. The user must learn to see, understand and remember the different pictogram symbols. There are about l, 400 different symbols at the present time.

    A Canadian named Subhas Maharaj came up with the idea for pictograms in the beginning of the 1980s. At first, pictograms were introduced to help people who had disabilities in speaking, reading, or writing. Pictograms are images of objects that are easy to see and create. Today, pictograms are used in many different ways. FOR example, there are traffic, recycling and restaurant signs, even animal symbols and so on.

    Pictograms are usually in white against a black background. The combination of white against a black background creates extremely contrast (对比) , and this makes pictograms friendlier to users. A good example of a pictogram is the public toilet symbols for "men" and women", just like the one on the left. Pictograms are a useful method of communication, and people can have fun as they learn each pictogram.