What innovation under the Sung dynasty made trade quicker and easier?

Paper currency made trade quicker and easier because buyers and sellers could use lightweight money instead of carrying heavy coins or exchanging goods directly. The Sung dynasty was among the first governments to issue paper money. The spinning wheel helped make textiles, irrigation canals supported farming and transport, and woodblock printing reproduced texts, but none made everyday payment as convenient as paper currency.

AI-written and checked against the verified answer.