Read the following statements about sex determination. (i) In grasshopper, sex is determined by the XO type, and the males have one chromosome fewer than the females. (ii) Human males produce two kinds of sperms, so sex determination in humans is an example of male heterogamety. (iii) In birds, the females have a Z and a W chromosome, while the males have a pair of Z chromosomes. (iv) In the XO type, all the sperms carry an X chromosome. (v) In humans, the type of ovum decides the sex of the child. How many of the statements above are correct?