The memory non-upgrade

You have upgraded the memory in a computer from 1 gigabyte to 2 GB. For the upgrade, you replaced two 512 MB DIMMs with two 1 GB DIMMs. Unfortunately, when you boot the computer the BIOS memory check only shows 1 GB of RAM. What is the most likely cause of this problem?

A) The BIOS must be upgraded to recognize the upgraded memory

B) The BIOS must be reconfigured to recognize the upgraded memory

C) One of the memory sticks is faulty or the incorrect type

D) 1 GB memory cannot be installed in pairs

E) I was told there would be no math