The app builder should provision a Partial Data sandbox to the developer. A Partial Data sandbox can have up to 5 GB of data, which meets the requirement of having at least half a gigabyte of data. A Partial Data sandbox can also be refreshed every 5 days, which meets the requirement of refreshing after each three-day sprint. Option A is incorrect because a Developer sandbox can only have up to 200 MB of data, which does not meet the requirement. Option B is incorrect because a Full Copy sandbox can only be refreshed every 29 days, which does not meet the requirement. Option C is incorrect because a Developer Pro sandbox can only have up to 1 GB of data, which may not be enough for the requirement.