Which of the following is true of the ionization energy of the elements?

Which of the following is true of the ionization energy of the elements?
 a. Ionization energy generally decreases as we move left to right and decreases as we move top to bottom in the periodic table.
  b. Ionization energy generally decreases as we move left to right and increases as we move top to bottom in the periodic table.
  c. Ionization energy generally increases as we move left to right and decreases as we move top to bottom in the periodic table.
  d. Ionization energy generally increases as we move left to right and increases as we move top to bottom in the periodic table.