Why don't all cells demonstrate the presence of all intracellular structures?

All the cells don't have all of the intracellular structures because each and every cell do not need each and every intracellular structure. The plant cells have chloroplasts because they need to convert the light energy into chemical energy via the process of photosynthesis, the animal cells, however, have no such need, therefore, the animal cells do not have chloroplasts. Also, the erythrocytes do not have the cellular organelles in them which are present in the other body cells, because there is no need for the cellular organelles in them. The large vacuoles in plant cells is also a great example. The plants need the vacuoles for the metabolic processes, while most animal cells have no need for them.

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.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added