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B Practicing mastery in schools is now possible through technology, and necessary to foster academic and mental growth in students.

Explanation:

Sal Khan's speech (Let's Teach Mastery-Not Test Scores) tackles on the issue  about what most students face when it comes to the traditional way of teaching that relies on test scores. For him, practicing a concept over and over again is important before moving to the next concept or topic. This is called "mastery." It may sound impractical if this will be done to every student as teachers say the teaching will be more personalized.

However, Khan argued that with the tools and technology of these days, it becomes easier to practice mastery in school. This is an essential step that will allow the students to grow not only academically, but also mentally. This will allow them to focus on their potentials and believe that they can get there. It will allow fast-paced progress with the world's civilizations.

So, this explains the answer.