Matthew has been playing the clarinet for many years, and he can play musical scales without giving much thought to the finger positions involved in the process. Matthew's mastery of the clarinet is most likely a result of

A result of years of practice and playing the instrument

Explanation:

When a person immerses himself in a new activity, it is normal for him to initially experience difficulty mastering it, no matter if he is learning a sport or playing an instrument in principle it will be difficult. Over time and according to the skills that the person has, you can see how it is improving. You can see how that person is becoming stronger and has greater control over what he learns, which is due to the process in which he immersed himself from the beginning.

A person who keeps practicing something over time will become an expert which is due to continuous repetition. The person memorizes what he has to do and every time it will be easier for him to do what he has to do. Someone who practices soccer with time will be able to have better handling of the ball, will not need to look at the ball when he carries it with his foot and will have greater agility when moving, the same happens with the case of Matthew. Matthew is already able to play the clarinet without thinking much about the positions of his fingers since his skills in playing the clarinet have been strengthened and he can easily remember the notes due to the years of practice he has had.

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.