To prevail in a product liability lawsuit, can a plaintiff rely solely on the defective condition of the product when the defendant sold the product? why or why not ?

No they can't.

Because the defendant could make a very easy defense on the defective condition claim.

Since it is very unlikely that the purchasers record the whole buying process with camera, the defendant could argue that the defect is created by the buyers and the buyers would not be able to provide any prove to counter it.

answer: a. the kind of population living in your neighbourhood.

the census explorer data tool by the us census bureau allows the user to zoom in on any neighbourhood within the united states and find the kind of people residing in that by race and age.  

the tool needs to needs to be used twice – once in order to find what type of people reside in a neighbourhood, and then to see the age groups of the people in the same neighbourhood.