Which of the following events led to the beginning of the modern era

You didn't list choices, but if they are the same as I've seen with another posting of this question (), then your answer is:

Explanation:

The "modern era" in history was introduced by the Scientific Revolution and the Enlightenment, so from around 1500 to early 1800s.  The "early modern era" would be the beginning of the modern era, with thinkers like Francis Bacon and Rene Descartes sending intellectual history in a new direction.  The modern era was a movement forward to scientific thinking and searching for reasonable explanations and solutions, in contrast to the medieval era's adherence to traditions, superstitions and religious beliefs.

The invention of gunpowder happened in China already around AD 850, long before the start of the modern era.

The exploration of outer space and the creation of the Internet occurred in the 20th century, about 500 years after the modern era had begun.

tearing down the berlin wall.

the perimeter of a triangle is 69 cm. side a is 5 cm shorter than side b. side c is twice as long as side a. find the length of each side. i need to know how to do it in 2 equations.  

equations:

a = b-5

c = 2a

a + b + c = 69