The correct answer is option 4: Rig-Veda. The Rig-Veda is one of the four sacred Hindu scriptures, it is the world`s oldest existing literary work and it has recently been included in the UNESCO’s Memory of World Register.

Explaining each option:

Option 1: Abhidhamma Pitaka – It is the last of the three `baskets` or collections that make up the Tripitaka, the scriptures of Buddhism. This text has not been included in the UNESCO’s Memory of World Register.

Option 2: Mahabharata – It is an ancient epic, the longest known epic poem and it narrates the struggle between two groups of cousins in the Kurukshetra War. It also has not been included in the UNESCO’s Memory of World Register.

Option 3: Ramayana – It is an ancient Indian epic, attributted to saint Valmiki and narrates the life of Rama, the legendary prince of the Kosala Kingdom. Just like options one and two, Ramayana also has not been included in the UNESCO’s Memory of World Register.

Thus, the Rig-Veda is the correct answer as it was recently included in the UNESCO’s Memory of World Register.