A
Dry ice is CO2 in solid form, with a temperature of about -78.5℃.Unlike common ice, dry ice doesn't melt into a liquid . When dry ice melts, it turns into a gas. So when you see dry ice "smoking", it's frozen CO2 melting into its gaseous state. Dry ice is a popular matter in scientific experiments. It creates projects that look cool.
Experiment: Healthy dry ice popsicles（棒冰）
This dry ice experiment will catch people's eye, especially little kids' because the dry ice is going to be used to make what the young love to eat. It should take you about 10 minutes or less to have a frozen treat to enjoy.
Materials
One large block of dry ice
A large spoon
Popsicle sticks
One cup of your favorite juice
A tall glass filled with water
Directions
Use the large spoon to make a popsicle-shaped space in a block of dry ice. You can set the ice on a piece of cloth on your table to do this work. Of course, keep in mind that it's okay if it's not exactly popsicle-shaped.
Add a popsicle stick to the middle of the space so that when you pour in the liquid, it will freeze around the popsicle stick.
Hold the popsicle stick in place and wait a few minutes for your popsicle to harden. After several minutes, take away the popsicle from the block of dry ice and put it into a tall glass of water for a few seconds. Do this to warm up the popsicle just a bit. Otherwise, it will be too cold.
21.According to the text, what's the main difference between dry ice and common ice?
A. Their forms. B. Their shapes.
C. Their temperatures. D. Their states when they melt.
22. What's the first step to do the experiment?
A. To fill the tall glass with juice.
B. To pour the juice into the space.
C. To make space in the dry ice for juice.
D. To put a stick to the middle of the dry ice.
23. How does the dry ice work in the experiment?
A. It gives out "smoke". B. It is mixed in the juice.
C. It makes the juice freeze. D. It makes the popsicle look cool.
