If all of the telephone extensions in a certain company must be even numbers, and if each of the extensions uses all four of the digits 1, 2, 3, and 4, what is the greatest number of four-digit extensions that the company can have?  Choose the correct choice:
A) 4 B) 6 C) 12 D) 16 E) 24
Since the phone number must be even, the unit's digit can be either 2 or 4.   When the unit's digit is 2 --&gt; number of possibilities is 3! = 6   When the unit's digit is 4 --&gt; number of possibilities is 3! = 6   Largest number of extensions = 6 + 6= 
<gadget id="calculator">6 + 6</gadget>
<output>12</output>
12   Answer:12
<result>C</result>
If all of the telephone extensions in a certain company must be even numbers, and if each of the extensions uses all four of the digits 1, 2, 3, and 4, what is the greatest number of four-digit extensions that the company can have?