Cells were discovered in 1665 by Robert Hooke when he took a piece of cork and looked at it under a microscope. Cork is made up of dead cells but you are still able to see the cells which proved to be interesting to him. He described  _ as being made of something, just like a wall is made of bricks. He then called those bricks "cells". Due to the size of cells, it is nearly impossible to see them without the aid of a light microscope, but by using an electron microscope you'd be able to see cells in much greater detail. There's a cell theory which is made up of four basic ideas. First, cells are the building blocks of life. Second, cells are derived from other cells by division. Third, cells contain DNA (the blueprint for life). Fourth, the cell is the functioning unit of life, and the chemical reactions of life take place within cells. There are two types of cells, animal cells and plant cells. Plant cells differ from animal cells in many ways. Plant cells have a large central vacuole , with the nucleus  nearer to the side of the cell instead of in the middle like in animal cells. Another big difference is that plant cells can produce and store sugar as starch  while animal cells contain glycogen . It's noteworthy to mention that a cell cannot survive without the nucleus which acts as a type of control center; it runs the cells. The nucleus contains DNA, which in turn contains the cell's genes. These genes tell the cell how to grow. DNA contains the genetic blueprint that tells if you have blonde hair and blue eyes. The passage was written mainly to  _  .
introduce different microscopes tell the differences between animal cells and plant cells introduce basic knowledge of cells tell how to observe cells with the right tools
Question: Cells were discovered in 1665 by Robert Hooke when he took a piece of cork and looked at it under a microscope. Cork is made up of dead cells but you are still able to see the cells which proved to be interesting to him. He described  _ as being made of something, just like a wall is made of bricks. He then called those bricks "cells". Due to the size of cells, it is nearly impossible to see them without the aid of a light microscope, but by using an electron microscope you'd be able to see cells in much greater detail. There's a cell theory which is made up of four basic ideas. First, cells are the building blocks of life. Second, cells are derived from other cells by division. Third, cells contain DNA (the blueprint for life). Fourth, the cell is the functioning unit of life, and the chemical reactions of life take place within cells. There are two types of cells, animal cells and plant cells. Plant cells differ from animal cells in many ways. Plant cells have a large central vacuole , with the nucleus  nearer to the side of the cell instead of in the middle like in animal cells. Another big difference is that plant cells can produce and store sugar as starch  while animal cells contain glycogen . It's noteworthy to mention that a cell cannot survive without the nucleus which acts as a type of control center; it runs the cells. The nucleus contains DNA, which in turn contains the cell's genes. These genes tell the cell how to grow. DNA contains the genetic blueprint that tells if you have blonde hair and blue eyes. The passage was written mainly to  _  .
A. introduce different microscopes
B. tell the differences between animal cells and plant cells
C. introduce basic knowledge of cells
D. tell how to observe cells with the right tools
Answer: