The default extension of MS Access (2007) file is:

.accdb

The correct answer is option 1- .accdb.

In Access 2007, the entire database is encompassed in a file (with extension .accdb) which can be stored in your hard-drive or CD. There can be multiple tables (each storing a specific set of data) with in this file. Then there are multiple fields in each table according to different categories (types) of data within the table. And at every instance (occurrence) of a collection of data covering all fields, a row/record gets created.