premise: A middle-aged man and woman ride bikes down a road beside the water. hypothesis: A couple is seen riding bikes.
entailment: One man plus one woman equals two people total; "a couple" refers to any group of two people.  A road is a transportation route, usually open to the public, for the express purpose of carrying traffic; should the couple ride down the road for long enough, they will almost surely encounter other traffic, which would be able to see them.  Also, bodies of water are generally flat, lacking hills, so anyone beside the water will be visible from quite a distance to anyone else on the water or on the other side of the body of water.