Pls hurry, i'm timed TmT Read this excerpt from "Why Are They Called Black Holes?"

Black holes are invisible because they have so much gravity that nothing escapes. Not even light can escape or bounce off. So how do scientists know that black holes exist if they are invisible?

Gravity is caused by matter, and as matter increases, the pull of gravity increases too. Stars are born when enough matter collects that gravity makes it collapse into a hot, dense protostar.

According to the introduction, why are black holes invisible?

Scientists can not figure out why they exist.
Gravity is caused by matter.
They have so much gravity that nothing escapes.
Stars are created first.

True or false when elements combine to form a mixture, the resulting chemical properties may be very different from those of the elements that make it.

In the nineteenth century, gregor mendel first determined some basic rules of genetics that have been observed throughout all types of life. no observations have disproved these basic rules of genetics. charles darwin developed the idea of biological evolution around the same time, but he was unaware of mendel’s discoveries in genetics. over a century later, darwin’s idea of evolution was modified in order to incorporate mendel’s rules of genetics along with the other evidence that darwin had used. what is most likely the relationship between mendel’s rules of genetics and darwin’s idea of biological evolution? a.)mendel’s genetics states laws that are now part of the theory of biological evolution.b.)biological evolution states laws that are part of mendel’s theory of genetics.c.)mendel’s genetics replaced darwin’s entire concept of biological evolution.d.)biological evolution is a law that explains why all genetics exist.

Calculate the first and second velocities of the car with four washers attached to the pulley, using the formulas v1 = 0.25 m / t1 , and v2 = 0.25 m / (t2 – t1) where t1 and t2 are the average times the car took to reach the 0.25 and the 0.50 meter marks. record these velocities, to two decimal places, in table e.