The model of systems development where each step is completed before proceeding down to the next step is known as:

Select one:

a. Stair-step model

b. Waterfall model

c. Agile model

d. SCRUM model

Answer:b) Waterfall model

Explanation: Waterfall model is the sequential structure in linear manner in which each stage of the structure is dependent on the components delivered from the previous stage. The next level carries out the task in correspondence with the previous one's specialized function. It is most commonly used in the software engineering field.

Other options are incorrect because stair-case model in which each stage is in the form of steps, agile model is the model focused on customer's need and splitting them into different incremental parts and and scrum model is represented by sprint sequence. Thus, the correct option is option (b).