I found DDR ram is not the answer in the demo questions from the comptia website execpt the rambus ram is the only answer.
second question: I only have to choose one if the question have not say this question is multiple .
RAMBus needs either a matched pair or a single stick and a special terminator stick called a continuity card. You can spot it right away because the RIMM stick will have a non-removable full length heatsink and you will have this funny little board in the next slot. Inexperienced tech seem to like to remove it and fail to put it back or in the wrong place until they ponder why memory does not work.
DDR can be used in singles unless you want to use the dual channel logic of your motherboard. Was that what you were looking for?
edit - to answer how many do you check? If the answers have round places then only one answer is possible. If they have squares then two or more answers are required and CompTIA tests normally tell you how many you must check.
However has anyone ever seen a motherboard that supported the newer revisions. I thought they were mostly for playstations. Intel had dropped RIMMs like a hot potato by then also being the primary chipset maker.