$9.$ True or False: The placement of counterweights on the crankshaft has no impact on the primary balance of an engine.

$10.$ True or False: Modal balancing can address multiple vibration modes simultaneously.

$11.$ True or False: Unbalance in a rotor can only be corrected by adding mass.

$12.$ True or False: Turbo machinery often requires special considerations for balancing due to the high pressures involved.