The correct answer is A. repetition.
Repetition is a control structure that allows a program to execute a block of code multiple times. This is often necessary when a program needs to perform a task a certain number of times or until a certain condition is met.
Selection is a control structure that allows a program to choose between two or more possible paths of execution. This is often necessary when a program needs to make a decision based on some input or condition.
Sequence is a control structure that allows a program to execute a block of code in the order in which it is written. This is the simplest type of control structure and is used in every program.
Switching is a control structure that allows a program to choose between multiple possible paths of execution based on the value of a variable. This is often used when a program needs to handle different cases of a particular situation.
In conclusion, the correct answer is A. repetition. This is because repetition is a control structure that allows a program to execute a block of code multiple times. This is often necessary when a program needs to perform a task a certain number of times or until a certain condition is met.