The classroom compound microscope invented by -
A. Kepler and Galileo
B. Janssen & Janssen
C. Tolles and Abbe
D. Knoll and Ruska

Hint: The compound microscope is used for viewing the samples at a higher level of magnification (2000x). The simple microscope can only magnify up to 300x, so a compound microscope was invented for better magnification.

Complete answer:
A compound microscope is a microscope that utilizes multiple lenses to enlarge the image of a sample. Basically, it is used for the observation of the sample at high magnification.
The compound microscope used two types of lenses -
1. Eyepiece - lens attached to the top side of the device, used to view a real image form by the objective lens
2. Objective - lens fixed at the bottom side of the device, which is close to the object that is magnified.
Uses - Compound microscopes allow scientists to see microorganisms and cells. Today these microscopes are common in science classrooms and laboratories. Without them, we would not know about the presence of cells. Because of these microscopes, we are able to study DNA and RNA.
100 years ago, glasses were invented. Scientists used grinding glasses, then Roman used glasses. They experimented with different shapes of clear glass and one of their samples was thick in the middle and thin on the edges. They discovered that if you held one of these “lenses” over an object, the object would look larger.
1. Hans and Zaccharias Janssen - Were the first men who developed the concept of the Compound Microscope. In the 1590s Dutch lens maker - Hans and Zaccharias Janssen (father and son) designed the device that can magnify objects. They used several lenses and placed them in the tube.
2. Galileo Galilei - In 1609, Galileo started the experiment - improvement on compound microscopes by his own. He describes the principle of the lenses and light rays. He called his device “little eye" or an occhiolino.
3. Robert Hooke - also known as the "English Father of Microscopy". He also works on the improvement on microscope designed. Hooke proposed the cell theory. He explored the structure, snowflakes, fleas, lice and plants.
4. Antoine van Leeuwenhoek - who is re - known as "the father of microscopy". In the 1670s he designed the single lens microscope, which can magnify up to 270X. With the help of this device he describes the sperm cells, bacteria, blood cells and yeast.
5. Ernst Ruska & Dr. Max Knoll - Ruska and his adviser Knoll were the first men who invented the electron microscope.

So, the correct answer is (B) Janssen & Janssen.

Note: In the 20th century, today the microscope becomes more stable and smaller in size. Its help resolved all the optical issues, which were common in the earlier version.