Which of the following factors in the simplified Drake equation is least well known?

Which of the following factors in the simplified Drake equation is least well known?
 
  A) Nhp, the number of habitable planets in our galaxy
  B) fciv, fraction of life-bearing planets where intelligent civilizations have arisen at any time
  C) fnow, fraction of civilization-bearing planets that have intelligent civilizations on them now
  D) flife, fraction of life-bearing habitable planets

Question 2

Suppose you wish to lower the pitch of a violin string by 2 octaves. This could be done by
 
  A) reducing the string tension by a factor of four.
  B) shortening the string length to a quarter as much.
  C) replacing the string with one of the same material only half as massive.
  D) replacing the string with one of the same material but with quadruple the diameter.
  E) increasing the string tension a factor of four.

Question 3

A container of an ideal gas at 1 atm is compressed to one-third its volume, with the temperature held constant. What is its final pressure?
 
  What will be an ideal response?

Question 4

A device that produces electricity by transforming chemical energy into electrical energy is called a
 
  A) generator.
  B) transformer.
  C) battery.
  D) none of the given answers