I am no grammer lord :-), but my 2c ->
1.
A - wrong tense (have developed) since the development took place in the past
B and D are wrong as the evidence if of development and not of American-Indians
C - The pronoun 'them' seems to refer to North American indians.
E is correct
2.
B - Seems to specify that 'dwellings that must also operate like business' have a distinction that is shared by the houses, but does not specify what that distinction is. Change in meaning makes this incorrect.
Also, number does not agree (dwellings v/s business)
C - Number does not agree (dwellings v/s business)
E - changes meaning. Also 'to be' and 'that' are inappropriate
Between A and D, I would choose A because I feel 'distinction of' is better than 'distinction that'
3.
A does not say who or what understands sytax
D seems to suggest that the syntax is in light of evidence
E - 'according to evidence' is at the wrong place. It should be placed between 'yet' and 'they'. At its present location, 'according to the evidence' seems to be modifying syntax
B - 'there is yet' seems to be wrong, although I can't explain why. 'their having understood' is not parallel to 'have a remarkable memory'
C - Is correct