In a chemical reaction, the reactants are substances that undergo the reaction, and the products are substances that are formed during the reaction. The table below shows the reactants and products of several different chemical reactions. Reactants Products Type of Reaction
4K + O2 2K2O + heat Exothermic
2H2O + heat 2H2 + O2 Endothermic
2CO + O2 2CO2 + heat Exothermic
CaCO3 + heat CaO + CO2 Endothermic

Based on the information given in the above table, the best definition of an endothermic reaction would be
A.
a reaction that absorbs heat.
B.
a reaction that has one product.
C.
a reaction that does not require heat.
D.
a reaction that releases heat.