A four-cylinder in-line reciprocating engine is shown in the Fig. 63 given below. The cylinders are numbered 1 to 4 and the firing order is 1-4-2-3:

Which one of the following statements is correct?

(a) Both primary and secondary forces are balanced

(b) Only primary force is balanced

(c) Only secondary force is balanced

(d) Both primary and secondary forces are unbalanced.

2 3 a a 3 Fig.63 Primary cranks