Which effect do rapidly cooling temperatures have on the water cycle? OPTIONS:
- Water droplets evaporate into vapor.
- Water vapor condenses into droplets.
- Condensation evaporates into precipitation.
- Precipitation condenses into water droplets.
A: Water vapor condenses into droplets.

In the human kidney, urea from the blood is filtered through the glomerular membrane into a nephron. The movement of urea across this membrane occurs without an input of energy. Which factor is the most likely reason urea absorption does not require energy? OPTIONS:
- a pH imbalance
- a pressure difference
- a temperature increase
- a concentration gradient
A: a concentration gradient

A scientist uses angstrom units to measure the distance between two points. The scientist is most likely measuring the distance between two OPTIONS:
- atoms.
- cities.
- continents.
- stars.
A: atoms.

Which a molecular process found only in retroviruses? OPTIONS:
- reverse translation
- translation
- reverse transcription
- transcription
A:
reverse transcription