What can be the limiting factors?

my experiment entails testing for enzymes with the use of test tubes. we had 3 test tubes labelled A B and C and we added 2g of crushed apple to each. then HCL, Sodium hydroxide solution and distilled water were added to each of them respectivley. then hydrogen peroxide was added to each one. Only C containing water fizzed to realease O2 gas. then we had to measure the height of the fizz. wut cud be a limiting factor this experiment?