Which of the following actions of the human body causes defaecation?

The correct option is B Involuntary action of the internal anal sphincter and Voluntary action of the external anal sphincter
The process of release of stool:-

1) Stretch detecting nerve present at the rectum sense that it is full.

2) The internal sphincter opens up and makes a contact of the content of rectum with the external sphincter.

3) When it has come in contact with external sphincter is depends on the person he wants to release or stop by either relaxing the puborectalis muscle or by contracting it.

So the correct option is 'Involuntary action of the internal anal sphincter and Voluntary action of the external anal sphincter'.