How Do Scientists Estimate How Old the Universe Is

Multiple Choice

How do scientists estimate how old the universe is?

A) They look up the answer in a book.
B) They measure the abundances of radioactive elements in meteorites, and use their half-lives to calculate the age.
C) They measure how fast the Sun is losing energy, and how much energy it has to lose.
D) They make a guess: no one really knows how old the universe is.
E) They measure the speeds and distances of galaxies, and calculate the time it took for them to travel that distance.