What is the value of the Trigger.old context variable in a Before Insert trigger?

What are two characteristics related to formulas? Choose 2 answers.

A developer needs to create a custom button for the Account object that, when clicked, will perform a series of calculation and redirect the user to a custom visualforce page.
Which three attributes need to be defined with values in the <apex:page> tag to accomplish this?
Choose 3 answers

As a part of class implementation a developer must execute a SOQL query against a large data ser based on the contact object. The method implementation is as follows.

Which two methods are best practice to implement heap size control for the above code? (Choose 2 Answers)

A developer needs to confirm that an Account trigger is working correctly without changing the organization's data.What would the developer do to test the Account trigger?