Which statement about the temperature dependence of the rate constant, K, is true for most chemical reactions?

a. k increases or decreases with temperature, depending on whether the reaction is endothermic or exothermic.
b. k increases with temperature, because the activation energy is usually positive.
c. k decreases with temperature, because a larger fraction of the molecules stay in a favorable orientation for the reaction.
d. k increases with temperature, because most spontaneous reactions are exothermic.
e. k decreases with temperature, because products are formed more quickly at higher temperature.