The use of the transient keyword In Visualforce Page Controllers helps with which common performance issued?

A company uses a custom-built enterprise resource planning (ERP) system to handle order management. The company wants Sales Reps to know the status of orders so that if a customer calls to ask about their shipment, the Sales Rep can advise the customer about the order's status and tracking number if it is already shipped.
Which two methods can make this ERP order data visible in Salesforce? Choose 2 answers

This sales team needs a custom Visualforce page to enter sales orders. When a product is selected on the Visualforce page, a web service is invoked to determine if the product is in stock, and the result is displayed on the page.
How can a developer write this page to display the result of the web service and ensure governor limits for concurrent usage are not exceeded?

Which use case can only be performed by using asynchronous Apex?

A developer writes the following Apex trigger so that when a Case is closed, a single Survey record is created for that Case. The issue is that multiple Survey_c records are being created per Case.

What could be the cause of this issue?