The correct option is indeed "1 and 3 only." The Amaravati Stupa, located in the lower Krishna valley, is significant for its intricate architectural design and sculptural reliefs, placing it as one of the prominent stupas of ancient India, though it is generally considered to be larger or comparable to Sanchi in importance rather than size. The Amaravati school of sculpture, known for its unique and detailed relief work, indeed influenced later South Indian sculpture and was instrumental in the dissemination of Buddhist art to Sri Lanka and Southeast Asia, illustrating the cultural exchanges facilitated by Buddhism in ancient times.