英语流利说懂你英语 Level4 Unit3 Part4 Voc
Civil wars are fought between citizens of the same country, and are fought within the country.
If citizens of a country disagree about a policy or leader, they may fight a civil war.
A world war is fought when countries form alliances, and these alliances fight each other.
A world war involves many or most of the world's most powerful countries.
There were 2 world wars in the 20th century.
Terrorism involves groups of individuals rather than countries.
Terrorists may come from different countries, and they may share the same beliefs.
Terrorists often use car bombings and suicide attacks on innocent people.
A terrorist attack can happen at any time and any place.
An invasion occurs when one country attacks another.
It sends its army into the other country, and attempts to take control.
One of the most famous invasions was when France invaded Russia in 1812.
A defensive war occurs when a country is attacked and needs to defend itself.
Most countries have a military, so that it can defend itself if it's attacked.
When France invaded Russia in 1812 the Russian army fought a defensive war and defeated the French army.
A cell is the basic unit of life.
The cell is the smallest structure that can live and reproduce.
Cells grow and develop, reproduce and interact with the environment.
Photosynthesis is one of the most important biological processes.
It allows plants to capture and use light as an energy source.
Photosynthesis is the process of converting light energy into chemical energy.
A virus is a small biological structure that attacks and enters cells.
Once inside a cell, a virus reproduces and makes many copies of itself.
Some diseases such as influenza are viruses.
Bacteria are one-celled forms of life that are all around us.
Although they have a single-cell structure, they are very important.
Many bacteria are inside us, and help us digest our food.
DNA is a complex molecule that stores information and can make copies of itself.
Nearly every cell in a person's body has the same DNA.
The information stored in DNA tells cells what to do, and is necessary for reproduction.
(Throughout history there have been many invasions.)
(There are billions of bacteria in our intestines.)
(The influenza virus spreads through the air when people cough or sneeze.)
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