Explanation/Reference:
Explanation:
Forward error control involves transmitting additional redundant information with each character or frame to facilitate detection and correction of errors, in feedback error control, only enough additional information is transmitted so the receiver can identify that an error has occurred.
Choices B and D are both error detection methods but not error correction methods. Block sum check is an extension of parity check wherein an additional set of parity bits is computed for a block of characters. A cyclic redundancy check is a technique wherein a single set of check digits is generated, based on the contents of the frame, for each frame transmitted.

Explanation/Reference:
Explanation: Selecting the right kind of data is key in testing a computer system. The data should not only include valid and invalid data but should be representative of actual processing; quality is more important than quantity. It is more important to have adequate test data than to complete the testing on schedule. It is unlikely that a random sample of actual data would cover all test conditions and provide a reasonable representation of actual data.

Section: Information System Operations, Maintenance and Support

Prototype systems can provide significant time and cost savings; however, they also have several disadvantages. They often have poor internal controls, change control becomes much more complicated, and it often leads to functions or extras being added to the system that were not originally intended.