A little girl runs out to the backyard where her father is working, and asks him, "Daddy, what's Sex?"
"OK," he thinks, "this day was bound to come, and I'm not going to let my little princess learn about sex from the streets."
So, he sits her down, and tells her all about the birds and the bees. He tells her about conception, intercourse, puberty and menstruation.
Then she asks, "Daddy, what is 'A Couple'?"
And he carries on, "A couple is two people like your mom and me." And he goes on to describe gay, lesbianism, etc...
The father finally asks, "So why did you want to know about 'a couple' and 'Sex'?"
"Oh, mummy said lunch would be ready in a couple of secs..." the girl replies.
Moral: If you don't understand the question properly, even the well-described answers are useless.