Suppose that $$f(x) = \ln(4 + x^2)$$

(A) Use interval notation to indicate where $f(x)$ is concave up.
Note: When using interval notation in WeBWorK, you use I for $\infty$, -I for $-\infty$, and U for the union symbol. If there are no values that satisfy the required condition, then enter "{}" without the quotation marks.

Concave up:

(B) Use interval notation to indicate where $f(x)$ is concave down.
Concave down:

(C) Find all inflection points of $f$. If there are no inflection points, enter -1000. If there are more than one, enter them separated by commas.
Inflection point(s) at $x$ =