The correct answer is B. Jon was surprised when it did not take him long to learn three cords on the guitar.
Step-by-step explanation:
The words "chord" and "cord" might seem similar but these have different meanings and therefore should be used in different contexts. In the case of the word "cord", this refers to a thin rope or string; on the other hand, the word "chord" refers to a set of musical notes.
In this way, the sentence "Jon was surprised when it did not take him long to learn three cords on the guitar" contains an error in word usage because in instruments including guitars you learn the "chords" (set of notes) but instead the word "cord" has been added which does not fit in this context, as the sentence refers to the musical notes rather than to the strings on the guitar.