The correct answer is A) Increased trade along China's eastern coast.
The development of hybrid plant species and advances in irrigation methods led to this effect during the Tang dynasty: Increased trade along China's eastern coast.
During the Tang Dynasty, irrigation advances played a key role to farm the lands and produce quality crops that were traded with other regions. In particular, the peaceful times during the Tang Dynasty allowed Chinese farmers to focus on producing crops that were important for the Dynasty as was the case of rice. Agriculture became stronger with irrigation techniques when farmers started to grow tea. Emperors were very proud of agriculture, made great profits and this also was a symbol of power.
