Teacher: 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.
Teacher: Now, understand the problem? If you are still confused, see the following 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.
Solution: why doesn't an optical mouse work on a glass
table?
Reason: 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.

Now, solve this instance: While historically the use of the semicolon and colon were similar, modern usage seems to be diverging, with semicolons indicating breaks slightly stronger than commas and colons introducing lists and explanations.
Semicolons have always been used in a manner very similar to commas, but with greater "weight." That is, the semicolon introduces greater breaks in the sentence, dividing clauses which are longer and more independent, while commas are reserved for short pauses and for separating lists of short items.
Continuing up the continuum, colons are "weightier" than semicolons, but less so than periods. They introduce a break which is longer or more important than that introduced by semicolons, but not as final as periods. Colons separate clauses which can stand as independent sentences grammatically, while semicolons can also be used for non-sentential clauses.
However, in modern writing the colon is rarely used in this role as glorified semicolon. The colon has developed a specific semantics as a break separating an introduction from an explanation. For example, the colon is used after the salutation in formal letters. It is used to introduce quotes, separating the source from the quoted text. A colon is used to introduce a list, included bulleted lists. A colon is used to separate the parts in a multipart title, such as "Reading Lolita in Tehran: A Memoir in Books" or "Good to Great: Why Some Companies Make the Leap...And Others Don't".
Student:
When do you use a semicolon instead of a colon?