which of the following statement about catalysis is true?
1. a small amount of catalyst often affects the rate of a reaction for a long time
2. a catalyst is always chemically unchanged at the end of a reaction
3. the effect of a catalyst is often enhanced by adding promoters
4. a catalyst is always physically unchanged
5. a catalyst always speeds up the rate of chemical reaction

• A.1,2,3,4,5
• B.1,2,3
• C.2,3,4
• D.2,4