Your friend is trying to convince you that if the ligaments binding the bones together at your freely movable joints (such as your knee, shoulder, and hip joints) contained a higher percentage of elastic fibers, you would be much more flexible. is this true? if so, would this present any serious problems?

If ligaments comprise greater number of elastic fibers they would become more stretchy, therefore, the joints would turn out more flexible. Though the prime role of the ligaments is to join bones together in a secured manner so that proper monitored movement of joint can take place.  

The presence of greater number of elastic ligaments would lead to floppy joints in which the bones taking part in the joint would become more vulnerable to dislocation and misalignment.  

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.

the answer is 100% density i've answered this question before and done the quiz myself.