Problem:OPTIONS:
- hours
- decades
- months
- H20
- Joules
- DNA
- years
- seasons

You are presented with the quiz "what unit of time can be estimated by the rings in a tree trunk?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "the number of rings in a tree trunk can be used to estimate the age of the tree" and "age of Pine trees (AGE) in years". So, what's the best answer to the question?
****
A: years

Problem:OPTIONS:
- Smoking
- sodium
- Dehydration
- sweating
- death
- birth
- Veins and arteries.
- lack of oxygen

You are presented with the quiz "what causes brain atrophy?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "brain cells die quickly if their oxygen supply is cut off" and "brain atrophy means the brain matter has shrunk, often because brain cells are dying or dead". So, what's the best answer to the question?
****
A: lack of oxygen

Problem:OPTIONS:
- earth's rotation
- scattered light
- earth's bend on rotating axis
- exposure to cold
- depress neuronal excitability
- earth's tilt on rotating axis
- wind and erosion
- earth's tilt on rotating half

You are presented with the quiz "What causes yearly temperature variations?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "the Earth being tilted on its rotating axis causes seasons" and "latitude and season cause temperature variations". So, what's the best answer to the question?
****
A: earth's tilt on rotating axis

Problem:OPTIONS:
- Alcohol
- lipids
- water
- spring
- coffee
- Energy.
- sugar
- energy

You are presented with the quiz "What forms into liquid from the air?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "condensing causes a liquid to form" and "condensation is water from the air". So, what's the best answer to the question?
****
A:
water