The correct answer is: A. at the beginning of each function.
Declaring variables at the beginning of each function makes the code more readable and easier to maintain. It also helps to avoid name collisions, which can occur when two variables have the same name in different scopes.
Option B is incorrect because declaring variables globally can make the code more difficult to read and maintain. It can also lead to name collisions, as mentioned above.
Option C is incorrect because declaring variables on one line can make the code difficult to read and understand. It can also make it difficult to find and modify variables, as they are all grouped together on one line.
Option D is incorrect because declaring variables with cryptic names can make the code difficult to read and understand. It can also make it difficult to find and modify variables, as they are not easily recognizable.
In conclusion, programmers prefer to declare almost all variables at the beginning of each function. This makes the code more readable and easier to maintain. It also helps to avoid name collisions.