Which of these is an example of an achievement of ancient india?

vaccination against smallpox during the gupta empire
adoption of buddhism as state religion of the gupta empire
first use of coins as money during the mauryan empire
abolishment of the military under the mauryan empire

Explanation:

Amid the Gupta dynasty (fourth to sixth century), Mahayana Buddhism turned progressively ritualistic, while Buddhist ideas were embraced into Hindu schools. The contrasts among Buddhism and Hinduism obscured, and Vaishnavism, Shaivism, and other Hindu conventions turned out to be progressively well known, while Brahmins built up another association with the state.  

As the system developed, Buddhist religious communities step by step lost control of land income. In parallel, the Gupta rulers manufactured Buddhist sanctuaries, for example, the one at Kushinagara, and religious colleges, for example, those at Nalanda, as prove by records left by three Chinese guests to India.

supplies had to travel a long distance across water on ships that were often attacked, so they did not reach europe

a. the astrolabe could determine the correct latitudinal location of the ship