Complete the statement to describe the calcium concentration that must be maintained in human body cells. ( fill in the blank )The calcium concentration must be greater ( blank ) the cell than ( blank ) the cell.

Which statement is true about a catalyst? a: a catalyst decreases the rate of the reaction. b. a catalyst is consumed during a chemical reaction. c. a catalyst lowers the activation energy of a reaction. d. a catalyst increases the reactant concentration during a reaction.