What is the meaning of the Greek root Osteo ?
it means Bone
Footsteps 100% sure because out of the 2 picks it is the only one in the phrase
The troposphere is the lowest level of the atmosphere, so it is in contact with the Earth's surface. In contrast, the stratosphere is located above the troposphere, so it is not in contact with the Earth's surface. ... The air density and air pressure are much lower in the stratosphere.