The correct answer is: D. a and b only
Structured design is a method of program design that uses top-down decomposition and stepwise refinement to break down a program into smaller and smaller modules until each module performs a single, well-defined task. This makes structured programs easier to understand, maintain, and test.
Option A is correct because structured programs are easier to maintain. This is because the modules in a structured program are independent of each other, so changes to one module do not affect other modules. This makes it easier to make changes to a structured program without affecting its overall functionality.
Option B is also correct because structured programs are easier to understand. This is because the modules in a structured program are organized in a logical way, and each module has a single, well-defined purpose. This makes it easier to read and understand a structured program.
Option C is incorrect because structured programs are not necessarily tested in a bottom-up fashion. In fact, top-down testing is often used for structured programs. Top-down testing involves testing the modules at the top of the program hierarchy first, and then testing the modules at the bottom of the hierarchy. This approach is often more efficient than bottom-up testing because it allows you to test the most important modules first.
Option E is incorrect because structured design does produce computer programs that are easier to maintain and understand.