What Benjamin Franklin invented?
A) Bifocal spectacles.
B) Radio
C) Barometer
D) Hygrometer

Hint: Mankind’s history is full of great discoveries. This question asks us about the discovery which was made by the great scientist Benjamin Franklin. Among the given options, bifocal spectacles is the correct option. In this discussion, we will discuss the invention and use of bifocals.

Complete step by step solution:
Some major discoveries of Benjamin Franklin are
1. Bifocal spectacles
2. Glass armonica
3. Lightning rod
4. Street lamps
5. Odometer
6. Flexible urinary catheter
7. Swimming fins
8. Franklin stove
Here, the bifocal lens among the options has been invented by Benjamin Franklin. So, let's have a brief discussion about bifocal spectacles.

Bifocals are eyeglasses with separate upper and lower half. The upper half is for distance and the lower half is for reading. In other words, bifocals are eyeglasses with two distinct optical powers. Bifocals are commonly prescribed to people with presbyopia who also require correction for myopia, hypermetropia and astigmatism.
Franklin’s eyesight was getting worse as he was getting older and he grew both nearsighted and farsighted which is the most common problem as suffered by most individuals. Tired of switching between lenses, he invented “double spectacles” which we now call as bifocals.
He had lenses from his two pairs of glasses. One for reading and other for distance. He sliced them in half horizontally and then remade them into a single pair, with lenses for distance at the top and the for reading at the bottom.

Note: Benjamin franklin was born on January 17,1790. He was an American statesman and scientist. He has also been known as “the First American”. He was a scientist who studied experiments in an effort to improve them or correct them.