How many primary partitions can exist on one drive?

Answer: Option B

On a traditional Master Boot Record (MBR) partitioning scheme, which is commonly used for BIOS-based systems, you can have a maximum of 4 primary partitions on one drive.
These primary partitions are used to define the basic structure of the disk and can be formatted with a file system to store data.
If you need more partitions, you can create extended partitions, which are special primary partitions that can hold multiple logical partitions within them.
However, with newer GUID Partition Table (GPT) partitioning schemes used on UEFI-based systems, you can have many more partitions, theoretically up to 128 partitions per disk.
So, in summary, on a traditional MBR partitioning scheme, you can have a maximum of 4 primary partitions on one drive.