F(x) is the same as "y". "interval" refers to the x-coordinates.
Now that you understand the terms, let's look at the questions.
(A) F(x) < 0 over interval (-∞, -4) ⇒ Are all of the y-coordinates less than zero between the x-coordinates of -∞ and -4? NO. All of the y-coordinates are positive.
(B) F(x) < 0 over interval (-∞, -3) ⇒ Are all of the y-coordinates less than zero between the x-coordinates of -∞ and -3? NO. Some of the y-coordinates are positive and some are negative.
(C) F(x) > 0 over interval (-∞, -3) ⇒ Are all of the y-coordinates greater than zero between the x-coordinates of -∞ and -3? NO. Some of the y-coordinates are positive and some are negative.
(D) F(x) > 0 over interval (-∞, -4) ⇒ Are all of the y-coordinates greater than zero between the x-coordinates of -∞ and -4? YES. All of the y-coordinates are positive.
Answer: D
