Ablack hole is
a - an empty region of space with a huge gravitational field
b - a small region that contains the mass of may galaxies
c - simply the remains of a giant star that has undergone gravitational collapse

A black hole is simply the remains of a giant star that has undergone gravitational collapse. As the statement mentioned in option A like empty region, that cannot be considered as correct one. Because the black holes, the region of space with high gravitational pull and formed after massive star collapse. So, correct answer would be C.

Option C

Explanation:

A black hole is a dense region in the space where the gravitational pull is maximum. Due to large amount of gravitational pull in that region, no matter even light cannot pass through the black hole. It is surrounded by very high energy and it even has the capacity to attract materials towards itself.

If a material enters the black hole, it will be completely destroyed. It is stated that black holes are formed by the gravitational collapse of giant stars after their decay.

So once the giant star decay they will collapse and their gravitational force will tend to condense the remains of the giant stars and they will be circulating with high gravitational pull forming the black holes.

answer: the exterior temperature of commercial jet planes as they leave the stratosphere and return to the ground increases steadily.

explanation:

the lower most layer of atmosphere is troposphere which extends from 0 to 12 km above the surface of the earth. the temperature initially decreases as distance is increased from the earth's surface. commercial jets fly in lower part of the stratosphere. the stratosphere extends upto 50 km. the temperature in stratosphere starts rising again due to presence of ozone which traps the uv rays.

thus, when the planes leave the stratosphere and return to the ground, the exterior temperature increases steadily.

  distance on the y-axis and time on the x-axis.

explanation:

the instantaneous velocity = change in position/time taken

the slope of the graph should give instantaneous velocity.

  slope of a graph = change in value of y -axis / change in values of x -axis

  comparing both the equations

    change in value of y -axis = change in position

  change in values of x -axis = time taken

so position values should be on the y axis and time values should be on the x axis.

distance on the y-axis and time on the x-axis.