Explanation:
The Rig Veda, Samaveda, Yajurveda, and Atharvaveda are the four ancient sacred texts of Hinduism known as the Vedas. They are considered the oldest religious scriptures in the world and form the foundation of Hindu philosophy, rituals, and hymns.

Later Vedic Books:
The later Vedic period refers to the period after the composition of the four Vedas. During this time, several other texts were written, known as the later Vedic books. These texts include the Brahmanas, Aranyakas, and Upanishads.

The Correct Answer:
The correct answer is option 'A' - 1 only. The Rig Veda is the oldest Veda and is considered the most important one. It is the earliest and most authoritative Vedic text, containing hymns and prayers dedicated to various deities. The other three - Samaveda, Yajurveda, and Atharvaveda - are also considered part of the earlier Vedic period.

Samaveda:
The Samaveda is a collection of melodies and chants derived from the Rig Veda. It is also one of the oldest religious texts and is primarily used for chanting during religious rituals and sacrifices.

Yajurveda:
The Yajurveda contains prose and verse formulas used during rituals and sacrifices. It provides detailed instructions on the proper performance of rituals, including the mantras and rituals to be followed.

Atharvaveda:
The Atharvaveda is a compilation of hymns, charms, and spells. It contains a wide range of content, including prayers for health, prosperity, and protection against evil spirits. It is considered the youngest of the four Vedas.

Conclusion:
In conclusion, the Rig Veda is the oldest and most important Veda, while the Samaveda, Yajurveda, and Atharvaveda are also part of the earlier Vedic period. Therefore, option 'A' - 1 only - is the correct answer as it correctly identifies the Rig Veda as not a later Vedic book.