Here's a short story:

The radian is the standard unit of angular measure, used in many areas of mathematics. The length of an arc of a unit circle is numerically equal to the measurement in radians of the angle that it s; one radian is just under 57.3 degrees (expansion at ). The unit was formerly an SI supplementary unit, but this category was abolished in 1995 and the radian is now considered an SI derived unit. 

Separately, the SI unit of solid angle measurement is the steradian. 

The radian is represented by the symbol rad. An alternative symbol is , the superscript letter c (for "circular measure"), the letter r, or a superscript , but these symbols are infrequently used as it can be easily mistaken for a degree symbol (°) or a radius (r). So, for example, a value of 1.2 radians could be written as 1.2 rad, 1.2 r, 1.2, or 1.2, or 1.2. 

Radian describes the plane angle subtended by a circular arc as the length of the arc divided by the radius of the arc. One radian is the angle subtended at the center of a circle by an arc that is equal in length to the radius of the circle. More generally, the magnitude in radians of such a subtended angle is equal to the ratio of the arc length to the radius of the circle; that is, , where "θ" is the subtended angle in radians, "s" is arc length, and "r" is radius. Conversely, the length of the enclosed arc is equal to the radius multiplied by the magnitude of the angle in radians; that is, . (End of story)

Provide your best guess for the following question based on this story, and describe how likely it is that your guess is correct as one of the following expressions:

Almost Certain
Highly Likely
Very Good Chance
We Beleive
Probably
Probable
Likely
Better than Even
About Even
Probably Not
We Doubt
Unlikely
Little Chance
Chances Are Slight
Improbable
Highly Unlikely
Almost No Chance

Give ONLY the guess and your confidence, no other words or explanation. For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>
Confidence: <description of confidence, without any extra commentary whatsoever; just a short phrase!>

Here are a few examples of questions and answers:

Question: What symbol represents the radian?
Guess: rad.
Confidence: <appropriate level of confidence in this guess>

Question: Are there any others?
Guess: yes
Confidence: <appropriate level of confidence in this guess>

Question: Are they frequently used?
Guess: no
Confidence: <appropriate level of confidence in this guess>

Question: Why?
Guess: but these symbols are infrequently used as it can be easily mistaken for a degree symbol (°) or a radius (r
Confidence: <appropriate level of confidence in this guess>

Question: What does the term describe?
Guess: the plane angle subtended by a circular arc
Confidence: <appropriate level of confidence in this guess>

Question: Is it used in many areas?
Guess: yes
Confidence: <appropriate level of confidence in this guess>

Question: What is equal to the measurement in radians?
Guess: The length of an arc of a unit circle
Confidence: <appropriate level of confidence in this guess>

Question: What was the units former classification?
Guess: an SI supplementary unit
Confidence: <appropriate level of confidence in this guess>

Question: Does that category still exist?
Guess: no
Confidence: <appropriate level of confidence in this guess>

Question: What happened to it?
Guess: it was abolished
Confidence: <appropriate level of confidence in this guess>

Question: When?
Guess: 1995
Confidence: <appropriate level of confidence in this guess>

Question: What is the category it is in now?
Guess: an SI derived unit.
Confidence: <appropriate level of confidence in this guess>

Now answer the following question in the same format.

Question: What is a steradian?

the SI unit of solid angle measurement