According to the Scrum Guide, the amount of work required of the Developers to complete a Product Backlog item selected during the Sprint Planning is as much as is required to meet the Scrum Team’s Definition of Done. This means that the Developers must ensure that every item they work on is in a usable condition and meets all quality standards agreed upon by the team. The other options are not valid descriptions of the amount of work required, as they are either too vague (such as all development work and some testing or a proportional amount of time) or incorrect (such as fitting as much as possible or deferring work to the next Sprint).