In subduction zones, dense pieces of oceanic crust are pulled downward toward the mantle. what is the result of this?

Volcanic eruption

During plate tectonics, the continental and oceanic plates collides. The oceanic plates being lighter gets submerged under continental plate. The subducted oceanic plate reaches the deep layers of the earth crust. The magma  present in the earth mantle melts the bottom layer of the subducted plate. The pores are formed on the subducted plate, the hot magma diffuses inside the plate. The plate becomes bouyant as the density of plate decreases. If the magma solidifies in the subducted plate, it will not have any impact on the surrounding water, if it remain in the molten stage can cause underwater volcanic eruption.

your spelling is a little off : ]

the correct answer is - d. china has a large and growing population.

the fact that china has a large (the biggest) population, and it is still growing, doesn't hinder the agriculture production in the country. in fact, it can for increased production in the agriculture, since there's more labor force, as well the sheer mass of people produces lots of scientists that come up with new inventions as to how to improve this sector. nice example is the inner mongolia region in china, in general dominated by the gobi desert, but few scientist came up with a nice idea as to how to make the region productive by using plants that are very resistant to droughts, so lots of people have been employed, and the region is becoming greener and greener each year, and the production of food in this region is also increasing.