Which quality allows programmers to modify a program as and when required?

A. Portability

B. Structure

C. Generally

D. Flexibility

A. Portability

Explanation:

Portability in computer programming is understood as capability of a program to be used in operating environment other than the one in which it was initially constructed.

A portable computer program can be run on different machines, having different operating environment, without making any major changes to program.

Program's portability allows programmer to make modification in programs as per need.

Hence the correct option is A. Portability.

Option B i. e. structure of a program is related to its overall presentation and organization.

Option C and D i ... e generally and flexibility have no relevance here and are not used as keywords in context of computer programming.