Which three code segments should you insert in sequence…

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.)
Select and Place:

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.