Which situation prevents a developer from setting sharing rules for a custom object?

A developer writes the following code:

What is the result of the debug statement?

A method is passed a list of generic sObjects as a parameter.
What should the developer do to determine which object type (Account, Lead, or Contact, for example) to cast each sObject?

A developer needs to join data received from an integration with an external system with parent records in Salesforce. The data set does not contain the Salesforce IDs of the parent records, but it does have a foreign key attribute that can be used to identify the parent.
Which action will allow the developer to relate records in the data model without knowing the Salesforce ID?

A developer must troubleshoot to pinpoint the causes of performance issues when a custom page loads in their org. Which tool should the developer use to troubleshoot?