The two main memory types are

The two main types of internal semiconductor memory are ROM and RAM.

Primary and secondary is a broader division of all storage, not the two main memory chips.

Random and sequential describe access methods, not memory types.

All of the above is wrong because only one pairing names the two main types.

RAM is read write and volatile, while ROM is read mostly and non volatile.

Together they make up the main memory found on the system board.