Software Engineering is best described as （  ）.
A．the practice of designing, building, and maintaining off-the-shelf software from  prefabricated parts          
B．the practice of designing, building, and maintaining ad-hoc software without the use of formal methods
C．the practice of designing, building, and maintaining reliable and cost-effective software using standard techniques
D．the practice of designing, building, and maintaining fast and flexible software specifically for engineering applications