The great wall served largely as a first line of defense and warning and was not seen as an impenetrable barrier. what is there about this view of the great wall that suggests this fact

The famous Great Wall of China is considered to be the first line of defense and warning and was not even seen as an impenetrable barrier to those nomadic invaders and tribes. The view of the Great Wall was a vast plain of northern China that extends more than 300,000 sq. kilometers to the south.

Moreover, the region was comprised of coastal lowlands, Piedmont tablelands, highlands prairies and enormous mountains extending approximately 3170 miles from east to west. With this massive land mass and wide variations in climate and environmental factors such as unpredictable water currents in rivers, steppes, desert lands and impenetrable ridges,  it was truly a first line of defense of China.

the option which was not a function of missionaries in the northwest was the first one - they established posts for trading furs and other goods.

missionaries were sent around the world to spread religion and their knowledge and others - they were not merchants who sold furs and other goods.