How do scientists know that dark matter exist?

a. it absorbs radio waves

b. it emits electromagnetic radiation

c. it exerts a gravitational pull on other matter

d. it blocks the light coming from other objects

Scientists cannot directly observe dark matter, but they know it exists by C, the way it exerts a gravitational pull on other matter. Most of the cosmic entities like galaxies do not have enough observable matter within them to logically exist, i.e. the amount of matter they have can’t hold the galaxy together.

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.

when heated, the valance electrons increased their speed and transferred the heat from electron to electron.   i just took the test.