Which protocol should an Integration Architect utilize to create a secure channel between Salesforce and other system?

What are two reasons an existing custom field cannot be marked as External ID? Choose 2 answers

The Integration Team at Universal Containers is frustrated because the developers keep changing the data model and trigger behaviors during development, resulting in frequent rework and unexpected bugs lade in the development process. What two recommendations should a Technical Architect make to resolve this issue?
Choose 2 answers

Universal Containers is currently doing User Acceptance Testing for small changes in a Developer sandbox.
Users are complaining that allow release to production, some functionality is broken and performance is often negatively impacted.What is causing these complaints?

Universal Containers has built an integration using the SOAP API to load records from a back-office system into Salesforce. The records created in the back-office system must be loaded into Salesforce in almost real time, so a custommodule was written to identify CRUD events in the back-office system and perform sync with Salesforce. UC has several other systems that integrate with Salesforce through the SOAP API using separate integration users.What is a risk involved with this sort of integration?