Given a scientific passage and an answer, generate a question for the given answer.

Input: Consider Input: Passage: - For lenses, the distance from the center of the lens to the focus is . Focal lengths are positive for converging lens and negative for diverging lens. The distance from the center of the lens to the object in question is , where distances to the left of the lens are positive in sign. The distance from the center of the lens to the image is . This number is positive for real images (formed to the right of the lens), and negative for virtual images (formed to the left of the lens). Answer: focal lengths

Output: What lengths are positive for converging lens and negative for diverging lens?

Input: Consider Input: Passage: The Prokaryotic Cell Recall that prokaryotes (Figure 22.10) are unicellular organisms that lack organelles or other internal membrane-bound structures. Therefore, they do not have a nucleus but instead generally have a single chromosomea piece of circular, double-stranded DNA located in an area of the cell called the nucleoid. Most prokaryotes have a cell wall outside the plasma membrane. Answer: nucleoid

Output: Prokaryotic cells do not have a nucleus but instead generally have a single chromosome, a piece of double-stranded dna located in an area of the cell called the what?

Input: Consider Input: Passage: The continental shelf is the ocean floor nearest the edges of continents. It has a a gentle slope. The water over the continental shelf is shallow. Answer: continental shelf
Output: What do you call the gently sloped ocean floor nearest the edges of continents?