The computers those are capable of great processing speed and data storage, allowing multiple users...

Mainframes are high-capacity computers known for their powerful processing speed, extensive data storage, and ability to support hundreds or thousands of simultaneous users. They are typically used by large organizations for mission-critical applications such as bulk data processing, enterprise resource planning, and transaction processing.

Workstations (A) are personal or high-performance single-user computers.

Main computers (B) is not a formal term.

Supercomputers (C) are used for highly complex calculations, not general-purpose multi-user environments.