$6.$ In multi$-$cylinder inline engines, what primarily determines the effectiveness of the balance?

$-$ A$)$ The number of cylinders

$-$ B$)$ The crankshaft design

$-$ C$)$ The type of fuel injection

$-$ D$)$ The configuration of the intake manifold

$7.$ Which type of balance is most challenging in a V$-$engine due to its configuration?

$-$ A$)$ Static balance

$-$ B$)$ Dynamic balance

$-$ C$)$ Torque balance

$-$ D$)$ Radial balance