Consider the following statements regarding a high speed in-line engine with identical reciprocating parts with cranks spaced to give equal firing intervals: 1. All harmonic farces, except those which are multiples of half the number of cylinders, are balanced. 2. Couples are balanced if the engine is symmetrical about a plane normal to the axis of the cranks shaft. 3. In a four cylinder in-line engine, second and fourth harmonic forces are unbalanced whereas in a six cylinder in-line engine, second fourth and sixth harmonic forces are unbalanced. Of these statements:

• A. 1, 2 and 3 are correct
• B. 1 and 3 are correct
• C. 1 and 2 are correct
• D. 2 and 3 are correct