Do you like Physics or Chemistry？ Matter （物质） is always changing， either physically or chemically． If a material goes through a physical change， it is still the same material． During a chemical change， one kind of matter changes into another completely different kind of matter． For example， when we burn wood or cook fish， materials change． People use chemistry every day in the kitchen． The food we eat has many different natural chemicals． Many of the chemicals in food are necessary parts of a healthy diet．

    Much of the food we eat has been changed in some way from its original form． The changes that food undergoes may be chemical or physical． If a change does not affect the food's chemical composition， we call it a physical change． For example， melted （溶解的） cheese has gone through a physical change． It gets softer when it is heated but it is still the same type of material． Any change that changes the chemicals in the food is a chemical change． Bread contains carbohydrates， which are chemicals made up of carbon， hydrogen， and oxygen． When bread is baked （烘焙）， the carbohydrates break down into black carbon and water． The carbon gives the bread a dark color and a crunchy texture （质地）． The water goes into the air．

    To get a closer look at the chemistry of baking， let's watch how a carrot cake is made． The main steps of baking any cake are mixing the ingredients （材料） and baking them together． In the course of making cakes， the dry ingredients are mixed first． They are flour， sugar， salt， baking soda， baking powder and spices． Flour gives the cake structure． Sugar helps to make it sweet． Salt strengthens the cake batter． Baking powder and baking soda make the cake rise．

    Next， the carrots may be added to the cake． These help give the carrot cake its flavor， texture， and color． The other ingredients in the carrot cake are oil and eggs． The oil makes the cake tender and moist． Eggs serve two purposes﹣the whites help the cake to rise， while the yolks （蛋黄） give it a creamy texture． All of these ingredients form a mixture． This mixture can be separated into its different components （成分） although it is very difficult． Once the cake mixture is formed， it's poured into a cake pan and baked in an oven． The heat from the oven has caused chemical changes to take place． The cake is finished and the ingredients cannot be separated．

（1）The material doesn't change when we　　．

A． melt ice cream

B． burn paper

C． bake apple pies

D． cook beef

（2）What's the correct order of baking a carrot cake in the passage？　　

a． Carrots， oil and eggs are added．

b． The dry ingredients are mixed．

c． The mixture is baked in an oven．

d． Baking powder and soda make the cake rise．

e． Preparing some dry ingredients．

f． The heat from the oven causes chemical changes．

g． The ingredients cannot be separated．

h． The mixture is poured into a pan

A． b﹣a﹣h﹣f﹣g

B． b﹣h﹣c﹣d﹣f

C． e﹣d﹣c﹣a﹣g

D． e﹣c﹣a﹣g﹣d

（3）After reading the passage， we know that　　．

A． water and carbon can give the cake a dark color and a crunchy texture

B． people can separate the mixture of eggs and oil into different components

C． chemicals in different kinds of food that people eat are bad for their health

D． sugar and salt can't be put into the mixture to make a cake at the same time

（4）The passage mainly helps us to　　．

A． look at the steps of baking cakes closely

B． learn how to make carrot cakes at home

C． have a healthy diet with natural chemicals

D． understand physical and chemical changes