Different Pitch - Written, Sounding and Concert
by Samuel J John
What is the difference between
1. Written pitch
2. Sounding pitch
3. Concert pitch
In your picture above, the question refers to an instrument (the clarinet in Bb) that is transposing.
Some instruments in the orchestra like the clarinet, the trumpet etc. (see a helpful list of instruments that are transposing vs. in concert pitch here) are transposed. When they play a written "C" in the score, it sounds like a different note.
The written music for these transposing instruments must be written in a different key so that when they play they will sound the same as other instruments that have concert pitch.
Instruments that have concert pitch, like the piano or the violin, are non-transposing, and when they play a written note, it is exactly that note.
In your example, you don't need to figure out how the Clarinet in Bb actually sounds when playing the melody. You simply need to complete the melody that you already have a given beginning to. If a clarinet actually would play that melody it would sound a whole tone lower though.
You can read more about pitch on this page:
Best of luck with your test!