Correct answer: B. S3 Standard

Every object in Amazon S3 has an associated storage class, and S3 Standard is explicitly documented as the default: if you don't specify the storage class when you upload an object, Amazon S3 assigns S3 Standard. This makes the second option correct regardless of what prefix or key the object shares with other objects. S3 Intelligent-Tiering is a real storage class, but it must be deliberately selected at upload time or applied later through a lifecycle rule; it is never assigned automatically just because no class was specified. S3 Standard-Infrequent Access likewise requires an explicit choice and is not a fallback default. The storage class of other objects sharing a key prefix is irrelevant because S3 has no concept of folder-level storage class inheritance; each object's class is set independently per PutObject call, so the fourth option describes behaviour S3 does not have.

Source: AWS S3 documentation: Understanding and managing Amazon S3 storage classes — S3 Standard is the default storage class