Gospel. Gospel usually contains three part harmonies(divided by Alto, Soprano, and Tenor) and emphasizes triads.
I cannot see it that clearly so I cannot tell you I am sorry I could not help.
Explanation:
The answer is A. Vibraphones.
strings is the family that includes violins, cellos, guitars, etc.
brass includes trumpets and the tuba, etc.
percussion includes drums, tambourines, etc.
