Part 1. Definition
You are given a passage. You need to construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) its answer is the whole paragraph. Avoid creating questions that can be answered correctly without actually understanding the paragraph.
Part 2. Example
Optical mice use an LED and a camera to rapidly
capture images of the surface beneath the mouse.
The infomation from the camera is analyzed by a
DSP (Digital Signal Processor) and used to detect
imperfections in the underlying surface and
determine motion. Some materials, such as glass,
mirrors or other very shiny, uniform surfaces
interfere with the ability of the DSP to
accurately analyze the surface beneath the mouse.

Since glass is transparent and very uniform, the
mouse is unable to pick up enough imperfections in
the underlying surface to determine motion.
Mirrored surfaces are also a problem, since they
constantly reflect back the same image, causing
the DSP not to recognize motion properly. When the
system is unable to see surface changes associated
with movement, the mouse will not work properly.
Answer: why doesn't an optical mouse work on a glass
table?
Explanation: The passage talks about the glass and mirror surfaces beneath the optical mice and how the mouse is unable to pick up enough imperfections in the underlying surface to determine motion. The last line of the passage explains why the mouse will not work properly on these surfaces. Thus it is a positive example.
Part 3. Exercise
The current scientific theory holds that black holes are formed when stars of sufficient mass (about 3x the mass of our Sun) reach the end of their life and collapse down into a singularity, which is, in essence, an infinitely small point with a huge amount of gravity - gravity so powerful that not even light can escape it's pull if it gets too close. It is also thought that black holes can be formed from smaller masses if external energy/pressure is exerted to squeeze the mass into a singularity.
Not sure if there's any direct experimental evidence of creation, but there is evidence that they exist. Cosmologists use several different methods to detect blacks holes, such as by looking for light being bent and/or disappearing as it travels from remote stars towards us, and also by looking for bursts of x-rays that are given off as matter is sucked into the back hole and destroyed.
Fun fact: current evidence and theory suggests that the center of the Milky Way is a giant black hole that was formed as the densly packed stars in the center collapsed and sucked each other in.
Answer:
How a black hole is formed?