Please help with physioex 8.0 excersise 8 activity 4

Tube 1 investigated the action of bile on enzyme activity, and tube 2 examined lipase
activity without bile. Bile enhances fat digestion by lipase.
Yes, you can determine if activity occurred in tube 6 because the pH would drop below
pH 9.0. A small amount of fat digestion occurred because pH decreased from 9.0 to 8.97.
The optimim pH for lipase activity was pH 7.0.
Using a pH method to assay for activity at pH 2.0 does not work because the buffer is
already quite acidic. There could have been activity at pH 2.0 that was not detectable by
this method.
In theory, lipase would be active in the mouth because its pH optimum is relatively neutral.
However, it would not be active in the stomach because of the acidic pH condition.
The substrate is vegetable oil (fat). The subunit formed is fatty acid (and monoglycerides).

Thanks for the answers, howeve, it seems that your answers are for different questions. Do you have the answers for my questions, please???