Which of the following is the correct reason for the identification of sex of the animals A and B given in the picture?

• A

  A is male Ascaris, the posterior end is straight;  B is female Ascaris, posterior end is curved.

• B

  A is female Ascaris, the posterior end is straight.  B is male Ascaris, posterior end is curved.

• C

  A is female Ascaris, the posterior end is curved; B is male Ascaris

• D

  A is male Ascaris, the posterior end is curved; B is female Ascaris, the posterior end is straight.