Built in memory of computer is ............

Explanation:

Option (b) ROM (Read-Only Memory) is the correct answer. ROM is a fundamental type of built-in, non-volatile memory that stores essential system instructions (like the BIOS) required for the computer's operation from startup. Option (a) EROM is not a standard acronym (it's usually EPROM). Option (c) RAM (Random Access Memory) is also built-in but is volatile and temporary, not typically referred to as 'the' built-in memory for core functions in this general context. Option (d) PROM (Programmable Read-Only Memory) is a specific type of ROM. Option (e) E REM is not a standard memory type.