Which of the following statements are correct for mating gears with involute profiles?
(i) The pressure angle, from the start of the engagement to the end of the engagement, remains constant.
(ii) The pressure angle is maximum at the beginning of the engagement, reduces to zero at pitch point, starts decreasing and again becomes maximum at the end of the engagement.
(iii) The face and flank of the teeth are generated by a single curve and the normal to this curve at any point is tangent to the base circle of the gear.
(iv) The centre distance for a pair of mating gears can be varied within limits without altering the velocity ratio.
Select the correct answer using the code given below.
(a) 1, 3 and 4 (b) 1 and 3 only
(c) 2 and 4 only (d) 2,3 and 4