Need help with college geometry/advanced math!!?

Question

2. Explain Incidence Geometry

a. Why do we need this to expand on Euclid's first

four axioms.

b. What are some holes to Incidence geometry?

For instance, Euclidean geometry

has other properties that are traditionally

"obvious" or assumed. Why aren't Euclid's

1st four axioms and incidence geometry enough

to satisfy "obvious" or assumed properties in

Euclidean geometry.