In case of partial balancing of single-cylinder reciprocating engine, what is the primary disturbing force along the line of stroke?

(a) \(\mathrm{cmr} \omega^{2} \cos \theta\)

(b) \(\left(1-c^{2}\right) m r \omega^{2} \cos \theta\)

(c) \((1-c) m \omega^{2} r \cos 2 \theta\)

(d) \((1-c) m \omega^{2} r \cos 2 \theta\)

where, \(c=\) Fraction of reciprocating mass to be balanced; \(\omega=\) Angular velocity of crankshaft; \(\theta=\) Crank angle.