Your app needs to store the following information. for each type of information, decide whether you would use an array or a variable to store it:

a. all the messages a user has sent.
b. the highest score a user has ever reached on the app.
c. a username and password to unlock the app.

The answer is "option c".

Explanation:

In the question, It is defined that an array variable that stores the value. This variable is used to store more than one value or in programming terms, we can say that an array is a collection of the homogeneous elements, that means it will store similar type of value that is "text value or numeric value"if we would use an array to store all messages that are sent by the user, however, the highest value of the score is stored in variable that would be a better choice for a password/username.That's why option c is correct.