RAM

D.

The memory that stores the decompressed form of Cisco IOS software and the running configuration is DRAM (Dynamic Random Access Memory).

DRAM is a type of volatile memory that is used to store the running configuration and currently executing IOS software. This means that when the device is powered off, the contents of DRAM are lost.

Flash memory (option A) is a non-volatile memory used to store the IOS image and other files such as configuration files and security certificates. Flash memory is used to boot the router and load the IOS image.

ROM (Read-Only Memory) (option B) is also non-volatile memory, but it is used to store the router's bootstrap program (a small piece of software that is used to start up the router) and the most basic operating system functions. ROM is also used to store the router's power-on self-test (POST) and diagnostic routines.

NVRAM (Non-Volatile Random Access Memory) (option C) is a type of non-volatile memory used to store the startup configuration. The startup configuration is loaded into RAM during the boot process.

Therefore, the correct answer is D. DRAM.