Why do astronauts' muscles weaken in space?
a. they are overused
b. they work against a strong gravitational force
c. they are exposed to radiation
d. they do not work as hard

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.