Question

These are instructions for making invisible ink using baking soda.

Difficulty:	Easy
Time required	A few minutes
What you need	Baking soda  Paper    Water     Light bulb     Paintbrush Measuring cup    Purple grape juice
Here’s how:	There are at least two methods of using baking soda as invisible ink. Mix equal amounts of water and baking soda. Use a paintbrush to write a message onto white paper, using the baking soda solution (溶液) as “ink”. Allow the ink to dry. One way to read the message is to hold the paper up to a heat source, such as a light bulb. The baking soda will cause the writing in the paper to turn brown. The second way to read the message is to paint over the paper with purple grape juice. The message will appear in a different color.
Tips:	If you are using the heating method, avoid igniting (点燃) the paper. Baking soda and grape juice react with each other in an acid-base (酸碱) reaction, producing a color change in the paper. Grape juice concentrate (浓缩物) results in a more visible color change than regular grape juice.

1.______ is not needed for making invisible ink.

A. Baking soda    B. Paper

C. Water    D. Ink

2.What’s the function of the paintbrush?

A. To draw a picture.    B. To write a message onto the white paper.

C. To allow the “ink” to appear.    D. To help the“ink” dry.

3.Why will the message appear in a different color in the second way to read the message?

A. Because there is enough grape juice.

B. Because baking soda reacts with grape juice.

C. Because of the use of water.

D. Because of the special paper.

4.From the process, we can know that making invisible ink is ______.

A. very hard    B. not difficult

C. a little difficult    D. not easy

Answer

1. D

2. B

3. B

4. B

【解析】

本文是一篇说明文。文章通过介绍难度，所需时间，所需器材以及过程来说明如何使用小苏打制造隐形墨水。

1.细节理解题。根据文章What you need中Baking soda Paper Water Light bulb Paintbrush Measuring cup Purple grape juice 可知，所需要的材料不包括墨水。故选D。

2.细节理解题。根据文章Here’s how:中Use a paintbrush to write a message onto white paper, using the baking soda solution (溶液) as “ink”.可知画笔的功能是在白纸上写信息。故选B。

3.推理判断题。根据文章The second way to read the message is to paint over the paper with purple grape juice. The message will appear in a different color.以及Baking soda and grape juice react with each other in an acid-base (酸碱) reaction, producing a color change in the paper.可知，小苏打和葡萄汁在酸碱反应中相互作用，从而出现不同的颜色。答案为B。

4.细节理解题。根据第二行 Difficulty: Easy可知，easy和not difficult表达同一含义，所以制作隐形墨水并不难。故选B。