Answer:
A.
Step-by-step explanation:
Let's break it down,
B is incorrect because if the car couldn't be found because it was stolen, it would not be available for ready use of its owner, meaning that B would be wrong.
C is wrong because if the computer was available to use any time, no student would be using it all day, but the text depicts that another student would be using it. Thus, the computer wouldn't be ready or available for the future rendering C also incorrect.
A is correct because available means not otherwise occupied; free to do something. So, in this case, your boss was asking if you are free to work or unoccupied in anything else. Since you would not be occupied, you would be able to work on this given day, or vice versa.