The adjective in this sentence would be modifying the noun "arch" since the adjective (tall) is making the reader better understand certain characteristics of the arch.
The right answer is the increase of agricultural output, the Ming dinasty ruled China for almost 300 years (1368-1644) and enjoyed stability and prosperity, reforming the government and making more efficient use of the land, one of the things that made this increase possible was taxes, what excludes the third option. As for the first option, Ming government persecuted to some extent Christian and Muslims communities, and for the fourth, Tokugawa was a dinastic government in Japan, not China.
