The is (are) the facial feature(s) that best express(es) emotion on its own; the is (are) the facial feature(s) that best express(es) emotion as part of the whole face.

I believe the answer is: eyes;mouth
When we feel positive emotion, our eyes tend to be folded upward and when we feel negative emotions it would folded on the opposite direction.
The mouth in this process would only make the small expression displayed by the eyes become much more obvious.

question 1

the reasons for the global discontent in the early 1900s were the following:

desire for independence   was the main fight of many territories which were still under the control of colonial powers. dissatisfaction with peace terms of wwi . the best example is the case of germany, that was forced by the peace treaties to pay very expensive war reparations to the winners of wwi. some time later, german leaders broke relations and stopped recognizing the authority of those who imposed sanctions on their country, counting with the support of the population that was suffering the important economic consequences of the payment of reparations. overproduction of consumer goods which led to hyperinflation scenarios and very week currencies and economies.

question 2

the reasons for the great depression were the following, and these led to wall street crash in october 1929 and caused the subsequent great recession period.

high personal debt, that ended up with many bankrupt investors. falling stock price as everybody was getting rid of the stocks, many because they could not meet the amounts of money required by the margins that backed their investments.

question 3

italy: led by the fascists and benito mussolini   and promised to restore the greatness of the roman empire. germany: led by adolph hitler and the nazi party and conducted anti-jewish riots in austriajapan: was controlled by aggressive military leaders and invaded countries for their resources

2.