Final answer:
Unassigned lesson times (student ID is null) in a class schedule should appear as blank entries.
Step-by-step explanation:
In a class schedule, unassigned lesson times (student ID is null) typically appear as blank entries.
When generating a class schedule, each student is assigned to specific education programs and classes based on factors such as test scores, previous grades, or perceived ability. If a student has not been assigned to a lesson time, that time slot would be left blank as it does not belong to any specific student. This can happen if a student hasn't registered for a class or hasn't been assigned a class schedule yet.
Therefore, the correct answer is b) As blank entries.