Answer:
b is the answer tennis ball
One possible unstructured activity that promotes resistance training would be climbing playground equimpent - A.
This is by nature a unstructured ctivity. Furthermore, it promotes resistance training because you're forced to move and pull and push yourself.
The total resistance in a series circuit is equal to the sum of all resistors (R total = ΣRi).
R total = R1 + R2 + R3 = (3 + 4 + 5) Ω = 12 Ω
I believe it would be a musical note