Final answer:
Blocks are read one at a time in a sequential manner when performing a single-level index scan. The index determines the order of reading the blocks, which contain rows matching the query's criteria.
Step-by-step explanation:
When performing a single-level index scan, blocks are read one at a time in a sequential manner.
The index is used to determine the order in which the blocks are read. Each block contains a set of rows that match the criteria specified in the query.
By reading blocks sequentially, the database reduces the number of I/O operations required, resulting in improved performance.