The correct answer is: a) Basic unit for census data collection.
An enumeration block is the smallest geographic unit used for census data collection. It is a group of contiguous housing units that are close enough to be counted by a single census enumerator. Enumeration blocks are typically defined by streets, roads, or other physical features.
The other options are incorrect. Option b) is incorrect because an administrative division of a district is typically a larger geographic unit than an enumeration block. Option c) is incorrect because a geographical area assigned to a teacher is typically a smaller geographic unit than an enumeration block. Option d) is incorrect because the enumeration block is the basic unit for census data collection, not none of the above.