Given the graph of $y = f(x)$ below, at which of the marked $x$-values can the following statements be true?

(For each question, enter your answer as a comma-separated list, e.g., x1,x3,x5. Enter none if no points satisfy the given condition)
A. $f(x) < 0$ at $x =$
B. $f'(x) < 0$ at $x =$
C. $f(x)$ is decreasing at $x =$
D. $f'(x)$ is decreasing at $x =$
E. The slope of $f(x)$ is positive at $x =$
F. The slope of $f'(x)$ is positive at $x =$