Which three code segments should you insert in sequence at line 09?

DRAG DROP
You are developing an application that includes a class named Kiosk. The Kiosk class includes a static
property named Catalog. The Kiosk class is defined by the following code segment. (Line numbers
are included for reference only.)

You have the following requirements:
Initialize the _catalog field to a Catalog instance.
Initialize the _catalog field only once.
Ensure that the application code acquires a lock only when the _catalog object must be instantiated.
You need to meet the requirements.
Which three code segments should you insert in sequence at line 09? (To answer, move the
appropriate code segments from the list of code segments to the answer area and arrange them in
the correct order.)

Answer:

Explanation:
After taking a lock you must check once again the _catalog field to be sure that other threads didn’t
instantiated it in the meantime.