Match the following file extensions to the type of file they are associated with

Synchronized versions of the collections in the Java Collections API allow ________ at a time to access a collection that might be shared among several threads.

a. any number of threads b. only one thread c. a maximum of two threads d. None of the above.

The _______________ address is 48 bits long, providing more than 281 trillion MAC addresses.

Fill in the blank(s) with the appropriate word(s).